From 2483528d26a355b08f59f71a7f84473e8965bea2 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Tue, 19 Mar 2024 13:02:27 +0000
Subject: [PATCH 01/18] Fix NativeName  and DisplayName for browser.

---
 .../src/Interop/Browser/Interop.Locale.cs     |  2 +
 .../Globalization/CultureData.Browser.cs      | 16 ++++++++
 .../System/Globalization/CultureData.Icu.cs   | 15 ++++++-
 .../CultureInfo/CultureInfoNames.cs           | 34 +++++++++++-----
 src/mono/browser/runtime/corebindings.c       |  2 +
 src/mono/browser/runtime/exports-binding.ts   |  3 +-
 .../runtime/hybrid-globalization/locales.ts   | 40 ++++++++++++++++++-
 7 files changed, 97 insertions(+), 15 deletions(-)

diff --git a/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs b/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs
index c882d88afac25..e86d87521be5e 100644
--- a/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs
+++ b/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs
@@ -13,5 +13,7 @@ internal static unsafe partial class JsGlobalization
         internal static extern unsafe int GetFirstDayOfWeek(in string culture, out int exceptionalResult, out object result);
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         internal static extern unsafe int GetFirstWeekOfYear(in string culture, out int exceptionalResult, out object result);
+        [MethodImplAttribute(MethodImplOptions.InternalCall)]
+        internal static extern unsafe int GetNativeName(in string locale, in string culture, char* buffer, int bufferLength, out int exceptionalResult, out object result);
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
index fcc5943e7b766..1ccd4c4e6701e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
@@ -11,6 +11,22 @@ internal sealed partial class CultureData
     {
         private const int CULTURE_INFO_BUFFER_LEN = 50;
 
+        private unsafe string JSGetNativeName(string localeName, string? uiCultureName = null)
+        {
+            if (string.IsNullOrEmpty(localeName))
+                return "Invariant Language (Invariant Country)";
+
+            string cultureName = uiCultureName ?? localeName;
+            // the longest possible NativeName is 50 characters
+            char* buffer = stackalloc char[CULTURE_INFO_BUFFER_LEN];
+            int exception;
+            object exResult;
+            int resultLength = Interop.JsGlobalization.GetNativeName(localeName, cultureName, buffer, CULTURE_INFO_BUFFER_LEN, out exception, out exResult);
+            if (exception != 0)
+                throw new Exception((string)exResult);
+            return new string(buffer, 0, resultLength);
+        }
+
         private static unsafe CultureData JSLoadCultureInfoFromBrowser(string localeName, CultureData culture)
         {
             char* buffer = stackalloc char[CULTURE_INFO_BUFFER_LEN];
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
index 435e7ba9d45fd..fc34abb4b7bce 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
@@ -203,6 +203,12 @@ private string IcuGetLocaleInfo(LocaleStringData type, string? uiCultureName = n
             Debug.Assert(!GlobalizationMode.Invariant);
             Debug.Assert(!GlobalizationMode.UseNls);
             Debug.Assert(_sWindowsName != null, "[CultureData.IcuGetLocaleInfo] Expected _sWindowsName to be populated already");
+#if TARGET_BROWSER
+            if (type == LocaleStringData.NativeDisplayName)
+            {
+                return JSGetNativeName(_sWindowsName, uiCultureName);
+            }
+#endif
             return IcuGetLocaleInfo(_sWindowsName, type, uiCultureName);
         }
 
@@ -302,7 +308,14 @@ private unsafe string IcuGetTimeFormatString(bool shortFormat)
         // no support to lookup by region name, other than the hard-coded list in CultureData
         private static CultureData? IcuGetCultureDataFromRegionName() => null;
 
-        private string IcuGetLanguageDisplayName(string cultureName) => IcuGetLocaleInfo(cultureName, LocaleStringData.LocalizedDisplayName, CultureInfo.CurrentUICulture.Name);
+        private string IcuGetLanguageDisplayName(string cultureName)
+        {
+#if TARGET_BROWSER
+            return JSGetNativeName(CultureInfo.CurrentUICulture.Name, cultureName);
+#else
+            return IcuGetLocaleInfo(cultureName, LocaleStringData.LocalizedDisplayName, CultureInfo.CurrentUICulture.Name);
+#endif
+        }
 
         // use the fallback which is to return NativeName
         private static string? IcuGetRegionDisplayName() => null;
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs
index d2c0828bc6850..fdde2c84ab56b 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs
@@ -10,19 +10,31 @@ namespace System.Globalization.Tests
 {
     public class CultureInfoNames
     {
-        private static bool SupportFullIcuResources => (PlatformDetection.IsNotMobile && PlatformDetection.IsIcuGlobalization) || PlatformDetection.IsHybridGlobalizationOnApplePlatform;
+        private static bool SupportFullIcuResources =>
+            (PlatformDetection.IsNotMobile && PlatformDetection.IsIcuGlobalization) ||
+            PlatformDetection.IsHybridGlobalizationOnApplePlatform ||
+            PlatformDetection.IsBrowser;
+        
+        public static IEnumerable<object[]> SupportedCultures_TestData()
+        {
+            // Browser does not support all ICU locales but it uses JS to get the correct native name
+            if (!PlatformDetection.IsBrowser)
+            {
+                yield return new object[] { "aa", "aa", "Afar", "Afar" };
+                yield return new object[] { "aa-ER", "aa-ER", "Afar (Eritrea)", "Afar (Eritrea)" };
+            }
+            yield return new object[] { "en", "en", "English", "English" };
+            yield return new object[] { "en", "fr", "English", "anglais" };
+            yield return new object[] { "en-US", "en-US", "English (United States)", "English (United States)" };
+            yield return new object[] { "en-US", "fr-FR", "English (United States)", "anglais (\u00C9tats-Unis)" };
+            yield return new object[] { "en-US", "de-DE", "English (United States)", "Englisch (Vereinigte Staaten)" };
+            yield return new object[] { "", "en-US", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)" };
+            yield return new object[] { "", "fr-FR", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)" };
+            yield return new object[] { "", "", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)" };
+        }
 
         [ConditionalTheory(nameof(SupportFullIcuResources))]
-        [InlineData("en", "en", "English", "English")]
-        [InlineData("en", "fr", "English", "anglais")]
-        [InlineData("aa", "aa", "Afar", "Afar")]
-        [InlineData("en-US", "en-US", "English (United States)", "English (United States)")]
-        [InlineData("en-US", "fr-FR", "English (United States)", "anglais (\u00C9tats-Unis)")]
-        [InlineData("en-US", "de-DE", "English (United States)", "Englisch (Vereinigte Staaten)")]
-        [InlineData("aa-ER", "aa-ER", "Afar (Eritrea)", "Afar (Eritrea)")]
-        [InlineData("", "en-US", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)")]
-        [InlineData("", "fr-FR", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)")]
-        [InlineData("", "", "Invariant Language (Invariant Country)", "Invariant Language (Invariant Country)")]
+        [MemberData(nameof(SupportedCultures_TestData))]
         public void TestDisplayName(string cultureName, string uiCultureName, string nativeName, string displayName)
         {
             using (new ThreadCultureChange(null, CultureInfo.GetCultureInfo(uiCultureName)))
diff --git a/src/mono/browser/runtime/corebindings.c b/src/mono/browser/runtime/corebindings.c
index 1b0c0a809f63e..d37da93b57b4d 100644
--- a/src/mono/browser/runtime/corebindings.c
+++ b/src/mono/browser/runtime/corebindings.c
@@ -64,6 +64,7 @@ extern mono_bool mono_wasm_starts_with (MonoString **culture, const uint16_t* st
 extern mono_bool mono_wasm_ends_with (MonoString **culture, const uint16_t* str1, int32_t str1Length, const uint16_t* str2, int32_t str2Length, int32_t options, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_index_of (MonoString **culture, const uint16_t* str1, int32_t str1Length, const uint16_t* str2, int32_t str2Length, int32_t options, mono_bool fromBeginning, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_calendar_info (MonoString **culture, int32_t calendarId, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
+extern int mono_wasm_get_native_display_name (MonoString **locale, MonoString **culture, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_culture_info (MonoString **culture, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_first_day_of_week (MonoString **culture, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_first_week_of_year (MonoString **culture, int *is_exception, MonoObject** ex_result);
@@ -105,6 +106,7 @@ void bindings_initialize_internals (void)
 	mono_add_internal_call ("Interop/JsGlobalization::EndsWith", mono_wasm_ends_with);
 	mono_add_internal_call ("Interop/JsGlobalization::IndexOf", mono_wasm_index_of);
 	mono_add_internal_call ("Interop/JsGlobalization::GetCalendarInfo", mono_wasm_get_calendar_info);
+	mono_add_internal_call ("Interop/JsGlobalization::GetNativeName", mono_wasm_get_native_display_name);
 	mono_add_internal_call ("Interop/JsGlobalization::GetCultureInfo", mono_wasm_get_culture_info);
 	mono_add_internal_call ("Interop/JsGlobalization::GetFirstDayOfWeek", mono_wasm_get_first_day_of_week);
 	mono_add_internal_call ("Interop/JsGlobalization::GetFirstWeekOfYear", mono_wasm_get_first_week_of_year);
diff --git a/src/mono/browser/runtime/exports-binding.ts b/src/mono/browser/runtime/exports-binding.ts
index d2ff55bc088a7..cbd07f066217b 100644
--- a/src/mono/browser/runtime/exports-binding.ts
+++ b/src/mono/browser/runtime/exports-binding.ts
@@ -22,7 +22,7 @@ import { mono_wasm_compare_string, mono_wasm_ends_with, mono_wasm_starts_with, m
 import { mono_wasm_get_calendar_info } from "./hybrid-globalization/calendar";
 
 import { mono_wasm_get_culture_info } from "./hybrid-globalization/culture-info";
-import { mono_wasm_get_first_day_of_week, mono_wasm_get_first_week_of_year } from "./hybrid-globalization/locales";
+import { mono_wasm_get_native_display_name, mono_wasm_get_first_day_of_week, mono_wasm_get_first_week_of_year } from "./hybrid-globalization/locales";
 import { mono_wasm_browser_entropy } from "./crypto";
 import { mono_wasm_cancel_promise } from "./cancelable-promise";
 
@@ -107,6 +107,7 @@ export const mono_wasm_imports = [
     mono_wasm_index_of,
     mono_wasm_get_calendar_info,
     mono_wasm_get_culture_info,
+    mono_wasm_get_native_display_name,
     mono_wasm_get_first_day_of_week,
     mono_wasm_get_first_week_of_year,
 ];
diff --git a/src/mono/browser/runtime/hybrid-globalization/locales.ts b/src/mono/browser/runtime/hybrid-globalization/locales.ts
index 4330d0977e360..add695eacf5ca 100644
--- a/src/mono/browser/runtime/hybrid-globalization/locales.ts
+++ b/src/mono/browser/runtime/hybrid-globalization/locales.ts
@@ -3,11 +3,47 @@
 
 import { wrap_error_root, wrap_no_error_root } from "../invoke-js";
 import { mono_wasm_new_external_root } from "../roots";
-import { monoStringToString } from "../strings";
+import { monoStringToString, stringToUTF16 } from "../strings";
 import { Int32Ptr } from "../types/emscripten";
 import { MonoObject, MonoObjectRef, MonoString, MonoStringRef } from "../types/internal";
 import { normalizeLocale } from "./helpers";
 
+export function mono_wasm_get_native_display_name(locale: MonoStringRef, culture: MonoStringRef, dst: number, dstLength: number, isException: Int32Ptr, exAddress: MonoObjectRef) : number
+{
+    const localeRoot = mono_wasm_new_external_root<MonoString>(locale),
+        cultureRoot = mono_wasm_new_external_root<MonoString>(culture),
+        exceptionRoot = mono_wasm_new_external_root<MonoObject>(exAddress);
+    try {
+        const localeName = monoStringToString(localeRoot);
+        const cultureName = monoStringToString(cultureRoot);
+        if (!localeName || !cultureName)
+            throw new Error("Locale or culture name is null or empty.");
+
+        const [language, region] = cultureName.split("-");
+        const languageName = new Intl.DisplayNames([localeName], {type: "language"}).of(language);
+        const regionName = region ? new Intl.DisplayNames([localeName], {type: "region"}).of(region) : undefined;
+        const result = region ? `${languageName} (${regionName})` : languageName;
+
+        if (!result)
+            throw new Error(`Native display name for culture=${cultureName} is null or empty.`);    
+    
+        if (result.length > dstLength)
+            throw new Error(`Native display name for culture=${cultureName} exceeds length of ${dstLength}.`);
+
+        stringToUTF16(dst, dst + 2 * result.length, result);
+        wrap_no_error_root(isException, exceptionRoot);
+        return result.length;
+    }
+    catch (ex: any) {
+        wrap_error_root(isException, ex, exceptionRoot);
+        return -1;
+    }
+    finally {
+        cultureRoot.release();
+        exceptionRoot.release();
+    }
+}
+
 export function mono_wasm_get_first_day_of_week(culture: MonoStringRef, isException: Int32Ptr, exAddress: MonoObjectRef): number{
 
     const cultureRoot = mono_wasm_new_external_root<MonoString>(culture),
@@ -53,7 +89,7 @@ function getFirstDayOfWeek(locale: string)
     const weekInfo = getWeekInfo(locale);
     if (weekInfo)
     {
-        // JS's Sunday == 7 while dotnet's Sunday == 0
+        // JS"s Sunday == 7 while dotnet"s Sunday == 0
         return weekInfo.firstDay == 7 ? 0 : weekInfo.firstDay;
     }
     // Firefox does not support it rn but we can make a temporary workaround for it,

From e4f4ffcc0e5981ee762f0843559aa987a9efd897 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Tue, 19 Mar 2024 13:18:57 +0000
Subject: [PATCH 02/18] Nit - rever over-renaming.

---
 src/mono/browser/runtime/hybrid-globalization/locales.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mono/browser/runtime/hybrid-globalization/locales.ts b/src/mono/browser/runtime/hybrid-globalization/locales.ts
index add695eacf5ca..0841a8e02f5bf 100644
--- a/src/mono/browser/runtime/hybrid-globalization/locales.ts
+++ b/src/mono/browser/runtime/hybrid-globalization/locales.ts
@@ -89,7 +89,7 @@ function getFirstDayOfWeek(locale: string)
     const weekInfo = getWeekInfo(locale);
     if (weekInfo)
     {
-        // JS"s Sunday == 7 while dotnet"s Sunday == 0
+        // JS's Sunday == 7 while dotnet's Sunday == 0
         return weekInfo.firstDay == 7 ? 0 : weekInfo.firstDay;
     }
     // Firefox does not support it rn but we can make a temporary workaround for it,

From e438304e853898d5b20c89a64fd28b55a4e9bd3d Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Tue, 19 Mar 2024 18:51:21 +0100
Subject: [PATCH 03/18] Update
 src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs

Co-authored-by: Meri Khamoyan <96171496+mkhamoyan@users.noreply.github.com>
---
 .../src/System/Globalization/CultureData.Browser.cs           | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
index 1ccd4c4e6701e..0fea0dcae9583 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
@@ -19,9 +19,7 @@ private unsafe string JSGetNativeName(string localeName, string? uiCultureName =
             string cultureName = uiCultureName ?? localeName;
             // the longest possible NativeName is 50 characters
             char* buffer = stackalloc char[CULTURE_INFO_BUFFER_LEN];
-            int exception;
-            object exResult;
-            int resultLength = Interop.JsGlobalization.GetNativeName(localeName, cultureName, buffer, CULTURE_INFO_BUFFER_LEN, out exception, out exResult);
+            int resultLength = Interop.JsGlobalization.GetNativeName(localeName, cultureName, buffer, CULTURE_INFO_BUFFER_LEN, out int exception, out object exResult);
             if (exception != 0)
                 throw new Exception((string)exResult);
             return new string(buffer, 0, resultLength);

From 5dee365448f006414623783d235f0356b3d46e41 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Wed, 20 Mar 2024 17:55:40 +0000
Subject: [PATCH 04/18] Enable more tests and fix them - initialize english and
 native names on CultureInfo constructio

---
 .../src/Interop/Browser/Interop.Locale.cs     |  2 +-
 .../Globalization/CultureData.Browser.cs      | 56 +++++++++++---
 .../System/Globalization/CultureData.Icu.cs   |  4 +-
 .../src/System/Globalization/CultureData.cs   |  1 +
 .../CultureInfo/CultureInfoEnglishName.cs     | 13 ++--
 .../CultureInfo/CultureInfoNativeName.cs      |  5 +-
 .../System/Globalization/RegionInfoTests.cs   | 14 ++--
 src/mono/browser/runtime/corebindings.c       |  4 +-
 src/mono/browser/runtime/exports-binding.ts   |  4 +-
 .../runtime/hybrid-globalization/helpers.ts   |  4 +-
 .../runtime/hybrid-globalization/locales.ts   | 74 ++++++++++++++++---
 11 files changed, 138 insertions(+), 43 deletions(-)

diff --git a/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs b/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs
index e86d87521be5e..b831e72e70cdb 100644
--- a/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs
+++ b/src/libraries/Common/src/Interop/Browser/Interop.Locale.cs
@@ -14,6 +14,6 @@ internal static unsafe partial class JsGlobalization
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         internal static extern unsafe int GetFirstWeekOfYear(in string culture, out int exceptionalResult, out object result);
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
-        internal static extern unsafe int GetNativeName(in string locale, in string culture, char* buffer, int bufferLength, out int exceptionalResult, out object result);
+        internal static extern unsafe int GetLocaleInfo(in string locale, in string culture, char* buffer, int bufferLength, out int exceptionalResult, out object result);
     }
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
index 0fea0dcae9583..e8f2927fb4d72 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
@@ -10,27 +10,63 @@ namespace System.Globalization
     internal sealed partial class CultureData
     {
         private const int CULTURE_INFO_BUFFER_LEN = 50;
+        private const int LOCALE_INFO_BUFFER_LEN = 80;
 
-        private unsafe string JSGetNativeName(string localeName, string? uiCultureName = null)
+        private static CultureData JSInitLocaleInfo(string? localeName, CultureData culture)
         {
             if (string.IsNullOrEmpty(localeName))
-                return "Invariant Language (Invariant Country)";
+            {
+                culture._sEnglishLanguage = "Invariant Language";
+                culture._sNativeLanguage = culture._sEnglishLanguage;
+                culture._sEnglishCountry = "Invariant Country";
+                culture._sNativeCountry = culture._sEnglishCountry;
+                culture._sEnglishDisplayName = $"{culture._sEnglishLanguage} ({culture._sEnglishCountry})";
+                culture._sNativeDisplayName = culture._sEnglishDisplayName;
+            }
+            else
+            {
+                // ToDo: make sure we do not re-ask for it
+                // English locale info
+                (culture._sEnglishLanguage, culture._sEnglishCountry) = culture.JSGetLocaleInfo("en-US", localeName);
+                culture._sEnglishDisplayName = string.IsNullOrEmpty(culture._sEnglishCountry) ?
+                    culture._sEnglishLanguage :
+                    $"{culture._sEnglishLanguage} ({culture._sEnglishCountry})";
+                // Native locale info
+                (culture._sNativeLanguage, culture._sNativeCountry) = culture.JSGetLocaleInfo(localeName, localeName);
+                culture._sNativeDisplayName = string.IsNullOrEmpty(culture._sNativeCountry) ?
+                    culture._sNativeLanguage :
+                    $"{culture._sNativeLanguage} ({culture._sNativeCountry})";
+            }
+            return culture;
+        }
 
-            string cultureName = uiCultureName ?? localeName;
-            // the longest possible NativeName is 50 characters
-            char* buffer = stackalloc char[CULTURE_INFO_BUFFER_LEN];
-            int resultLength = Interop.JsGlobalization.GetNativeName(localeName, cultureName, buffer, CULTURE_INFO_BUFFER_LEN, out int exception, out object exResult);
+        private unsafe (string, string) JSGetLocaleInfo(string cultureName, string localeName)
+        {
+            char* buffer = stackalloc char[LOCALE_INFO_BUFFER_LEN];
+            int resultLength = Interop.JsGlobalization.GetLocaleInfo(cultureName, localeName, buffer, LOCALE_INFO_BUFFER_LEN, out int exception, out object exResult);
             if (exception != 0)
                 throw new Exception((string)exResult);
-            return new string(buffer, 0, resultLength);
+            string result = new string(buffer, 0, resultLength);
+            string[] subresults = result.Split("##");
+            if (subresults.Length == 0)
+                throw new Exception("LocaleInfo recieved from the Browser is in incorrect format.");
+            if (subresults.Length == 1)
+                return (subresults[0], ""); // Neutral culture
+            return (subresults[0], subresults[1]);
+        }
+
+        private string JSGetNativeDisplayName(string localeName, string cultureName)
+        {
+            (string languageName, string countryName) = JSGetLocaleInfo(localeName, cultureName);
+            return string.IsNullOrEmpty(countryName) ?
+                    languageName :
+                    $"{languageName} ({countryName})";
         }
 
         private static unsafe CultureData JSLoadCultureInfoFromBrowser(string localeName, CultureData culture)
         {
             char* buffer = stackalloc char[CULTURE_INFO_BUFFER_LEN];
-            int exception;
-            object exResult;
-            int resultLength = Interop.JsGlobalization.GetCultureInfo(localeName, buffer, CULTURE_INFO_BUFFER_LEN, out exception, out exResult);
+            int resultLength = Interop.JsGlobalization.GetCultureInfo(localeName, buffer, CULTURE_INFO_BUFFER_LEN, out int exception, out object exResult);
             if (exception != 0)
                 throw new Exception((string)exResult);
             string result = new string(buffer, 0, resultLength);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
index fc34abb4b7bce..32d26e35433fb 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
@@ -206,7 +206,7 @@ private string IcuGetLocaleInfo(LocaleStringData type, string? uiCultureName = n
 #if TARGET_BROWSER
             if (type == LocaleStringData.NativeDisplayName)
             {
-                return JSGetNativeName(_sWindowsName, uiCultureName);
+                return JSGetNativeDisplayName(_sWindowsName, uiCultureName ?? _sWindowsName);
             }
 #endif
             return IcuGetLocaleInfo(_sWindowsName, type, uiCultureName);
@@ -311,7 +311,7 @@ private unsafe string IcuGetTimeFormatString(bool shortFormat)
         private string IcuGetLanguageDisplayName(string cultureName)
         {
 #if TARGET_BROWSER
-            return JSGetNativeName(CultureInfo.CurrentUICulture.Name, cultureName);
+            return JSGetNativeDisplayName(CultureInfo.CurrentUICulture.Name, cultureName);
 #else
             return IcuGetLocaleInfo(cultureName, LocaleStringData.LocalizedDisplayName, CultureInfo.CurrentUICulture.Name);
 #endif
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
index 7013429ad4c0e..7a543a9ecacdd 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
@@ -822,6 +822,7 @@ private static string NormalizeCultureName(string name, out bool isNeutralName)
             {
                 culture = JSLoadCultureInfoFromBrowser(culture._sName, culture);
             }
+            culture = JSInitLocaleInfo(culture._sName, culture);
 #endif
 
             // We need _sWindowsName to be initialized to know if we're using overrides.
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs
index 02ee539981adb..5d040857b5fd0 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs
@@ -9,13 +9,14 @@ namespace System.Globalization.Tests
     public class CultureInfoEnglishName
     {
         // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-        public static bool SupportFullGlobalizationData => PlatformDetection.IsNotUsingLimitedCultures || PlatformDetection.IsAndroid;
+        // Browser uses JS to get the NativeName that is missing in ICU
+        public static bool SupportFullGlobalizationData => !PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform;
 
         public static IEnumerable<object[]> EnglishName_TestData()
         {
             yield return new object[] { CultureInfo.CurrentCulture.Name, CultureInfo.CurrentCulture.EnglishName };
 
-            if (SupportFullGlobalizationData || PlatformDetection.IsHybridGlobalizationOnApplePlatform)
+            if (SupportFullGlobalizationData)
             {
                 yield return new object[] { "en-US", "English (United States)" };
                 yield return new object[] { "fr-FR", "French (France)" };
@@ -41,12 +42,12 @@ public void EnglishName(string name, string expected)
         public void ChineseNeutralEnglishName()
         {
             CultureInfo ci = new CultureInfo("zh-Hans");
-            Assert.True(ci.EnglishName == "Chinese (Simplified)" || ci.EnglishName == "Chinese, Simplified",
-                        $"'{ci.EnglishName}' not equal to `Chinese (Simplified)` nor `Chinese, Simplified`");
+            Assert.True(ci.EnglishName == "Chinese (Simplified)" || ci.EnglishName == "Chinese, Simplified" || ci.EnglishName == "Simplified Chinese",
+                        $"'{ci.EnglishName}' not equal to `Chinese (Simplified)` nor `Chinese, Simplified` nor `Simplified Chinese`");
 
             ci = new CultureInfo("zh-HanT");
-            Assert.True(ci.EnglishName == "Chinese (Traditional)" || ci.EnglishName == "Chinese, Traditional",
-                        $"'{ci.EnglishName}' not equal to `Chinese (Traditional)` nor `Chinese, Traditional`");
+            Assert.True(ci.EnglishName == "Chinese (Traditional)" || ci.EnglishName == "Chinese, Traditional" || ci.EnglishName == "Traditional Chinese",
+                        $"'{ci.EnglishName}' not equal to `Chinese (Traditional)` nor `Chinese, Traditional` nor `Traditional Chinese`");
         }
     }
 }
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs
index 9a834dbf2d1db..c4fcc4e2ab495 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs
@@ -13,7 +13,8 @@ public static IEnumerable<object[]> NativeName_TestData()
             yield return new object[] { CultureInfo.CurrentCulture.Name, CultureInfo.CurrentCulture.NativeName };
 
             // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-            if (PlatformDetection.IsNotUsingLimitedCultures || PlatformDetection.IsAndroid || PlatformDetection.IsHybridGlobalizationOnApplePlatform)
+            // Browser uses JS to get the NativeName that is missing in ICU
+            if (!PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform)
             {
                 yield return new object[] { "en-US", "English (United States)" };
                 yield return new object[] { "en-CA", "English (Canada)" };
@@ -21,7 +22,7 @@ public static IEnumerable<object[]> NativeName_TestData()
             }
             else
             {
-                // Mobile / Browser ICU doesn't contain CultureInfo.NativeName
+                // WASI's ICU doesn't contain CultureInfo.NativeName
                 yield return new object[] { "en-US", "en (US)" };
                 yield return new object[] { "en-CA", "en (CA)" };
             }
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
index e05fd4e1a7422..602088d48e5f4 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
@@ -12,6 +12,8 @@ namespace System.Globalization.Tests
 {
     public class RegionInfoPropertyTests
     {
+        public static bool SupportFullGlobalizationData => !PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform;
+
         [Theory]
         [InlineData("US", "US", "US")]
         [InlineData("IT", "IT", "IT")]
@@ -112,7 +114,8 @@ public void DisplayName(string name, string expected)
         public static IEnumerable<object[]> NativeName_TestData()
         {
             // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-            if (PlatformDetection.IsNotUsingLimitedCultures || PlatformDetection.IsAndroid || PlatformDetection.IsHybridGlobalizationOnApplePlatform)
+            // Browser uses JS to get the NativeName that is missing in ICU
+            if (SupportFullGlobalizationData)
             {
                 yield return new object[] { "GB", "United Kingdom" };
                 yield return new object[] { "SE", "Sverige" };
@@ -120,7 +123,7 @@ public static IEnumerable<object[]> NativeName_TestData()
             }
             else
             {
-                // Browser's ICU doesn't contain RegionInfo.NativeName
+                // WASI's ICU doesn't contain RegionInfo.NativeName
                 yield return new object[] { "GB", "GB" };
                 yield return new object[] { "SE", "SE" };
                 yield return new object[] { "FR", "FR" };
@@ -134,10 +137,11 @@ public void NativeName(string name, string expected)
             Assert.Equal(expected, new RegionInfo(name).NativeName);
         }
 
-        public static IEnumerable<object[]> EnglishName_TestData()
+        public static IEnumerable<object[]> EnglishName_TestData() // this might be failing, in that case - fix it or block it
         {
             // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-            if (PlatformDetection.IsNotUsingLimitedCultures || PlatformDetection.IsAndroid || PlatformDetection.IsHybridGlobalizationOnApplePlatform)
+            // Browser uses JS to get the NativeName that is missing in ICU
+            if (SupportFullGlobalizationData)
             {
                 yield return new object[] { "en-US", new string[] { "United States" } };
                 yield return new object[] { "US", new string[] { "United States" } };
@@ -146,7 +150,7 @@ public static IEnumerable<object[]> EnglishName_TestData()
             }
             else
             {
-                // Browser's ICU doesn't contain RegionInfo.EnglishName
+                // WASI's ICU doesn't contain RegionInfo.EnglishName
                 yield return new object[] { "en-US", new string[] { "US" } };
                 yield return new object[] { "US", new string[] { "US" } };
                 yield return new object[] { "zh-CN", new string[] { "CN" }};
diff --git a/src/mono/browser/runtime/corebindings.c b/src/mono/browser/runtime/corebindings.c
index d37da93b57b4d..a4c1c0a7fb0c5 100644
--- a/src/mono/browser/runtime/corebindings.c
+++ b/src/mono/browser/runtime/corebindings.c
@@ -64,7 +64,7 @@ extern mono_bool mono_wasm_starts_with (MonoString **culture, const uint16_t* st
 extern mono_bool mono_wasm_ends_with (MonoString **culture, const uint16_t* str1, int32_t str1Length, const uint16_t* str2, int32_t str2Length, int32_t options, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_index_of (MonoString **culture, const uint16_t* str1, int32_t str1Length, const uint16_t* str2, int32_t str2Length, int32_t options, mono_bool fromBeginning, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_calendar_info (MonoString **culture, int32_t calendarId, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
-extern int mono_wasm_get_native_display_name (MonoString **locale, MonoString **culture, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
+extern int mono_wasm_get_locale_info (MonoString **locale, MonoString **culture, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_culture_info (MonoString **culture, const uint16_t* result, int32_t resultLength, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_first_day_of_week (MonoString **culture, int *is_exception, MonoObject** ex_result);
 extern int mono_wasm_get_first_week_of_year (MonoString **culture, int *is_exception, MonoObject** ex_result);
@@ -106,7 +106,7 @@ void bindings_initialize_internals (void)
 	mono_add_internal_call ("Interop/JsGlobalization::EndsWith", mono_wasm_ends_with);
 	mono_add_internal_call ("Interop/JsGlobalization::IndexOf", mono_wasm_index_of);
 	mono_add_internal_call ("Interop/JsGlobalization::GetCalendarInfo", mono_wasm_get_calendar_info);
-	mono_add_internal_call ("Interop/JsGlobalization::GetNativeName", mono_wasm_get_native_display_name);
+	mono_add_internal_call ("Interop/JsGlobalization::GetLocaleInfo", mono_wasm_get_locale_info);
 	mono_add_internal_call ("Interop/JsGlobalization::GetCultureInfo", mono_wasm_get_culture_info);
 	mono_add_internal_call ("Interop/JsGlobalization::GetFirstDayOfWeek", mono_wasm_get_first_day_of_week);
 	mono_add_internal_call ("Interop/JsGlobalization::GetFirstWeekOfYear", mono_wasm_get_first_week_of_year);
diff --git a/src/mono/browser/runtime/exports-binding.ts b/src/mono/browser/runtime/exports-binding.ts
index cbd07f066217b..af129e772c702 100644
--- a/src/mono/browser/runtime/exports-binding.ts
+++ b/src/mono/browser/runtime/exports-binding.ts
@@ -22,7 +22,7 @@ import { mono_wasm_compare_string, mono_wasm_ends_with, mono_wasm_starts_with, m
 import { mono_wasm_get_calendar_info } from "./hybrid-globalization/calendar";
 
 import { mono_wasm_get_culture_info } from "./hybrid-globalization/culture-info";
-import { mono_wasm_get_native_display_name, mono_wasm_get_first_day_of_week, mono_wasm_get_first_week_of_year } from "./hybrid-globalization/locales";
+import { mono_wasm_get_locale_info, mono_wasm_get_first_day_of_week, mono_wasm_get_first_week_of_year } from "./hybrid-globalization/locales";
 import { mono_wasm_browser_entropy } from "./crypto";
 import { mono_wasm_cancel_promise } from "./cancelable-promise";
 
@@ -107,7 +107,7 @@ export const mono_wasm_imports = [
     mono_wasm_index_of,
     mono_wasm_get_calendar_info,
     mono_wasm_get_culture_info,
-    mono_wasm_get_native_display_name,
+    mono_wasm_get_locale_info,
     mono_wasm_get_first_day_of_week,
     mono_wasm_get_first_week_of_year,
 ];
diff --git a/src/mono/browser/runtime/hybrid-globalization/helpers.ts b/src/mono/browser/runtime/hybrid-globalization/helpers.ts
index 1590936d8eacc..4cd1b9f4eb242 100644
--- a/src/mono/browser/runtime/hybrid-globalization/helpers.ts
+++ b/src/mono/browser/runtime/hybrid-globalization/helpers.ts
@@ -25,9 +25,9 @@ export function normalizeLocale(locale: string | null)
         const canonicalLocales = (Intl as any).getCanonicalLocales(locale.replace("_", "-"));
         return canonicalLocales.length > 0 ? canonicalLocales[0] : undefined;
     }
-    catch(ex: any)
+    catch
     {
-        throw new Error(`Get culture info failed for culture = ${locale} with error: ${ex}`);
+        return undefined;
     }
 }
 
diff --git a/src/mono/browser/runtime/hybrid-globalization/locales.ts b/src/mono/browser/runtime/hybrid-globalization/locales.ts
index 0841a8e02f5bf..d234810383e6e 100644
--- a/src/mono/browser/runtime/hybrid-globalization/locales.ts
+++ b/src/mono/browser/runtime/hybrid-globalization/locales.ts
@@ -6,29 +6,81 @@ import { mono_wasm_new_external_root } from "../roots";
 import { monoStringToString, stringToUTF16 } from "../strings";
 import { Int32Ptr } from "../types/emscripten";
 import { MonoObject, MonoObjectRef, MonoString, MonoStringRef } from "../types/internal";
-import { normalizeLocale } from "./helpers";
+import { OUTER_SEPARATOR, normalizeLocale } from "./helpers";
 
-export function mono_wasm_get_native_display_name(locale: MonoStringRef, culture: MonoStringRef, dst: number, dstLength: number, isException: Int32Ptr, exAddress: MonoObjectRef) : number
+export function mono_wasm_get_locale_info(culture: MonoStringRef, locale: MonoStringRef, dst: number, dstLength: number, isException: Int32Ptr, exAddress: MonoObjectRef) : number
 {
     const localeRoot = mono_wasm_new_external_root<MonoString>(locale),
         cultureRoot = mono_wasm_new_external_root<MonoString>(culture),
         exceptionRoot = mono_wasm_new_external_root<MonoObject>(exAddress);
     try {
-        const localeName = monoStringToString(localeRoot);
-        const cultureName = monoStringToString(cultureRoot);
+        const localeNameOriginal = monoStringToString(localeRoot);
+        const localeName = normalizeLocale(localeNameOriginal);
+        if (!localeName && localeNameOriginal)
+        {
+            // handle non-standard or malformed locales by forwarding the locale code
+            stringToUTF16(dst, dst + 2 * localeNameOriginal.length, localeNameOriginal);
+            wrap_no_error_root(isException, exceptionRoot);
+            return localeNameOriginal.length;
+        }
+        const cultureNameOriginal = monoStringToString(cultureRoot);
+        const cultureName = normalizeLocale(cultureNameOriginal);
+        
         if (!localeName || !cultureName)
-            throw new Error("Locale or culture name is null or empty.");
+            throw new Error(`Locale or culture name is null or empty. localeName=${localeName}, cultureName=${cultureName}`);
 
-        const [language, region] = cultureName.split("-");
-        const languageName = new Intl.DisplayNames([localeName], {type: "language"}).of(language);
-        const regionName = region ? new Intl.DisplayNames([localeName], {type: "region"}).of(region) : undefined;
-        const result = region ? `${languageName} (${regionName})` : languageName;
+        const localeParts = localeName.split("-"); // de-DE-u-co-phonebk-u-xx
+        // cultureName can be in a form of:
+        // 1) "language", e.g. "zh"
+        // 2) "language-region", e.g. "zn-CN"
+        // 3) "language-script-region", e.g. "zh-Hans-CN"
+        // 4) "language-script", e.g. "zh-Hans" (served in the catch block below)
+        let languageName, regionName;
+        try
+        {
+            const region = localeParts.length > 1 ? localeParts.pop() : undefined;
+            // this line might fail if form 4 from the comment above is used:
+            regionName = region ? new Intl.DisplayNames([cultureName], {type: "region"}).of(region) : undefined;
+            const language = localeParts.join("-");
+            languageName = new Intl.DisplayNames([cultureName], {type: "language"}).of(language);
+        }
+        catch (error)
+        {
+            if (error instanceof RangeError && error.message === "invalid_argument")
+            {
+                // it failed from this reason then cultureName is in a form "language-script", without region
+                try
+                {
+                    languageName = new Intl.DisplayNames([cultureName], {type: "language"}).of(localeName);
+                }
+                catch (error)
+                {
+                    if (error instanceof RangeError && error.message === "invalid_argument" && localeNameOriginal)
+                    {
+                        // handle non-standard or malformed locales by forwarding the locale code, e.g. "xx-u-xx"
+                        stringToUTF16(dst, dst + 2 * localeNameOriginal.length, localeNameOriginal);
+                        wrap_no_error_root(isException, exceptionRoot);
+                        return localeNameOriginal.length;
+                    }
+                    throw error;
+                }
+            }
+            else
+            {
+                throw error;
+            }
+        }
+        const localeInfo = {
+            LanguageName: languageName,
+            RegionName: regionName,
+        };
+        const result = Object.values(localeInfo).join(OUTER_SEPARATOR);
 
         if (!result)
-            throw new Error(`Native display name for culture=${cultureName} is null or empty.`);    
+            throw new Error(`Locale info for locale=${localeName} is null or empty.`);    
     
         if (result.length > dstLength)
-            throw new Error(`Native display name for culture=${cultureName} exceeds length of ${dstLength}.`);
+            throw new Error(`Locale info for locale=${localeName} exceeds length of ${dstLength}.`);
 
         stringToUTF16(dst, dst + 2 * result.length, result);
         wrap_no_error_root(isException, exceptionRoot);

From dceed892319da60855df33197f33fb796486f16a Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Wed, 20 Mar 2024 18:50:38 +0000
Subject: [PATCH 05/18] Ubnblock fixed test.

---
 .../System/Globalization/RegionInfoTests.cs                     | 1 -
 src/mono/browser/runtime/hybrid-globalization/locales.ts        | 2 +-
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
index 602088d48e5f4..b5da114ae4ba9 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
@@ -102,7 +102,6 @@ public void ValidateUsingCasedRegionName(string regionName)
         [Theory]
         [InlineData("en-US", "United States")]
         [OuterLoop("May fail on machines with multiple language packs installed")] // see https://github.com/dotnet/runtime/issues/30132
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/45951", TestPlatforms.Browser)]
         public void DisplayName(string name, string expected)
         {
             using (new ThreadCultureChange(null, new CultureInfo(name)))
diff --git a/src/mono/browser/runtime/hybrid-globalization/locales.ts b/src/mono/browser/runtime/hybrid-globalization/locales.ts
index d234810383e6e..821ebb3890397 100644
--- a/src/mono/browser/runtime/hybrid-globalization/locales.ts
+++ b/src/mono/browser/runtime/hybrid-globalization/locales.ts
@@ -29,7 +29,7 @@ export function mono_wasm_get_locale_info(culture: MonoStringRef, locale: MonoSt
         if (!localeName || !cultureName)
             throw new Error(`Locale or culture name is null or empty. localeName=${localeName}, cultureName=${cultureName}`);
 
-        const localeParts = localeName.split("-"); // de-DE-u-co-phonebk-u-xx
+        const localeParts = localeName.split("-");
         // cultureName can be in a form of:
         // 1) "language", e.g. "zh"
         // 2) "language-region", e.g. "zn-CN"

From d516e2dada889d17c35751f7e37d9450ed90f026 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Thu, 21 Mar 2024 09:16:45 +0000
Subject: [PATCH 06/18] MT does not work with HG well, revet MT to original way
 of working.

---
 .../src/System/Globalization/CultureData.Icu.cs       |  4 ++--
 .../src/System/Globalization/CultureData.cs           |  2 +-
 .../CultureInfo/CultureInfoEnglishName.cs             |  6 +++---
 .../CultureInfo/CultureInfoNames.cs                   |  6 +++---
 .../CultureInfo/CultureInfoNativeName.cs              | 10 ++++++----
 .../System/Globalization/RegionInfoTests.cs           | 11 ++++-------
 6 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
index 32d26e35433fb..31cc5bdd60155 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Icu.cs
@@ -203,7 +203,7 @@ private string IcuGetLocaleInfo(LocaleStringData type, string? uiCultureName = n
             Debug.Assert(!GlobalizationMode.Invariant);
             Debug.Assert(!GlobalizationMode.UseNls);
             Debug.Assert(_sWindowsName != null, "[CultureData.IcuGetLocaleInfo] Expected _sWindowsName to be populated already");
-#if TARGET_BROWSER
+#if TARGET_BROWSER && !FEATURE_WASM_MANAGED_THREADS
             if (type == LocaleStringData.NativeDisplayName)
             {
                 return JSGetNativeDisplayName(_sWindowsName, uiCultureName ?? _sWindowsName);
@@ -310,7 +310,7 @@ private unsafe string IcuGetTimeFormatString(bool shortFormat)
 
         private string IcuGetLanguageDisplayName(string cultureName)
         {
-#if TARGET_BROWSER
+#if TARGET_BROWSER && !FEATURE_WASM_MANAGED_THREADS
             return JSGetNativeDisplayName(CultureInfo.CurrentUICulture.Name, cultureName);
 #else
             return IcuGetLocaleInfo(cultureName, LocaleStringData.LocalizedDisplayName, CultureInfo.CurrentUICulture.Name);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
index 7a543a9ecacdd..47f87734558a1 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
@@ -816,7 +816,7 @@ private static string NormalizeCultureName(string name, out bool isNeutralName)
             {
                 return null;
             }
-#if TARGET_BROWSER
+#if TARGET_BROWSER && !FEATURE_WASM_MANAGED_THREADS
             // populate fields for which ICU does not provide data in Hybrid mode
             if (GlobalizationMode.Hybrid && !string.IsNullOrEmpty(culture._sName))
             {
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs
index 5d040857b5fd0..0868869622a63 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoEnglishName.cs
@@ -9,8 +9,9 @@ namespace System.Globalization.Tests
     public class CultureInfoEnglishName
     {
         // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-        // Browser uses JS to get the NativeName that is missing in ICU
-        public static bool SupportFullGlobalizationData => !PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform;
+        // Browser uses JS to get the NativeName that is missing in ICU (in the singlethreaded runtime only)
+        public static bool SupportFullGlobalizationData =>
+            (!PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform) && !PlatformDetection.IsWasmThreadingSupported;
 
         public static IEnumerable<object[]> EnglishName_TestData()
         {
@@ -24,7 +25,6 @@ public static IEnumerable<object[]> EnglishName_TestData()
             }
             else
             {
-                // Mobile / Browser ICU doesn't contain CultureInfo.EnglishName
                 yield return new object[] { "en-US", "en (US)" };
                 yield return new object[] { "fr-FR", "fr (FR)" };
             }
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs
index fdde2c84ab56b..b4ba35adb85e4 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNames.cs
@@ -10,10 +10,10 @@ namespace System.Globalization.Tests
 {
     public class CultureInfoNames
     {
+        // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
+        // Browser uses JS to get the NativeName that is missing in ICU (in the singlethreaded runtime only)
         private static bool SupportFullIcuResources =>
-            (PlatformDetection.IsNotMobile && PlatformDetection.IsIcuGlobalization) ||
-            PlatformDetection.IsHybridGlobalizationOnApplePlatform ||
-            PlatformDetection.IsBrowser;
+            !PlatformDetection.IsWasi && !PlatformDetection.IsAndroid && PlatformDetection.IsIcuGlobalization && !PlatformDetection.IsWasmThreadingSupported;
         
         public static IEnumerable<object[]> SupportedCultures_TestData()
         {
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs
index c4fcc4e2ab495..c61f8364e20c8 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/CultureInfo/CultureInfoNativeName.cs
@@ -8,13 +8,16 @@ namespace System.Globalization.Tests
 {
     public class CultureInfoNativeName
     {
+        // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
+        // Browser uses JS to get the NativeName that is missing in ICU (in the singlethreaded runtime only)
+        private static bool SupportFullIcuResources =>
+            (!PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform) && !PlatformDetection.IsWasmThreadingSupported;
+
         public static IEnumerable<object[]> NativeName_TestData()
         {
             yield return new object[] { CultureInfo.CurrentCulture.Name, CultureInfo.CurrentCulture.NativeName };
 
-            // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-            // Browser uses JS to get the NativeName that is missing in ICU
-            if (!PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform)
+            if (SupportFullIcuResources)
             {
                 yield return new object[] { "en-US", "English (United States)" };
                 yield return new object[] { "en-CA", "English (Canada)" };
@@ -22,7 +25,6 @@ public static IEnumerable<object[]> NativeName_TestData()
             }
             else
             {
-                // WASI's ICU doesn't contain CultureInfo.NativeName
                 yield return new object[] { "en-US", "en (US)" };
                 yield return new object[] { "en-CA", "en (CA)" };
             }
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
index b5da114ae4ba9..5783dd62b1997 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
@@ -12,7 +12,10 @@ namespace System.Globalization.Tests
 {
     public class RegionInfoPropertyTests
     {
-        public static bool SupportFullGlobalizationData => !PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform;
+        // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
+        // Browser uses JS to get the NativeName that is missing in ICU (in the singlethreaded runtime only)
+        public static bool SupportFullGlobalizationData =>
+            (!PlatformDetection.IsWasi || PlatformDetection.IsHybridGlobalizationOnApplePlatform) && !PlatformDetection.IsWasmThreadingSupported;
 
         [Theory]
         [InlineData("US", "US", "US")]
@@ -112,8 +115,6 @@ public void DisplayName(string name, string expected)
 
         public static IEnumerable<object[]> NativeName_TestData()
         {
-            // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-            // Browser uses JS to get the NativeName that is missing in ICU
             if (SupportFullGlobalizationData)
             {
                 yield return new object[] { "GB", "United Kingdom" };
@@ -122,7 +123,6 @@ public static IEnumerable<object[]> NativeName_TestData()
             }
             else
             {
-                // WASI's ICU doesn't contain RegionInfo.NativeName
                 yield return new object[] { "GB", "GB" };
                 yield return new object[] { "SE", "SE" };
                 yield return new object[] { "FR", "FR" };
@@ -138,8 +138,6 @@ public void NativeName(string name, string expected)
 
         public static IEnumerable<object[]> EnglishName_TestData() // this might be failing, in that case - fix it or block it
         {
-            // Android has its own ICU, which doesn't 100% map to UsingLimitedCultures
-            // Browser uses JS to get the NativeName that is missing in ICU
             if (SupportFullGlobalizationData)
             {
                 yield return new object[] { "en-US", new string[] { "United States" } };
@@ -149,7 +147,6 @@ public void NativeName(string name, string expected)
             }
             else
             {
-                // WASI's ICU doesn't contain RegionInfo.EnglishName
                 yield return new object[] { "en-US", new string[] { "US" } };
                 yield return new object[] { "US", new string[] { "US" } };
                 yield return new object[] { "zh-CN", new string[] { "CN" }};

From 20752cec30ceda6743583be85f685263d7bef603 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Thu, 21 Mar 2024 14:47:20 +0000
Subject: [PATCH 07/18] Expect fixed version of NativeName in tests with single
 treaded runtime.

---
 .../wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs     | 3 ++-
 src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs b/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
index 0fd604cfea6e2..79d3921a9442b 100644
--- a/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
@@ -141,10 +141,11 @@ await BlazorRunTest(new BlazorRunOptions()
         }
         else
         {
+            string nativeName = IsWorkloadWithMultiThreadingForDefaultFramework ? "es-ES" : "espa\u00F1ol (Espa\u00F1a)"; // MT does not use JS to get the full name
             Assert.DoesNotContain("Could not create es-ES culture", output);
             Assert.DoesNotContain("invalid culture", output);
             Assert.DoesNotContain("CurrentCulture.NativeName: Invariant Language (Invariant Country)", output);
-            Assert.Contains("es-ES: Is-LCID-InvariantCulture: False, NativeName: es (ES)", output);
+            Assert.Contains($"es-ES: Is-LCID-InvariantCulture: False, NativeName: {nativeName}", output);
 
             // ignoring the last line of the output which prints the current culture
         }
diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index 25f16fca67af4..7d43833e119e9 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -70,7 +70,9 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             else
             {
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
-                Assert.Contains("es-ES: Is Invariant LCID: False, NativeName: es (ES)", output);
+                Assert.Contains(IsWorkloadWithMultiThreadingForDefaultFramework ?
+                    "es-ES: Is Invariant LCID: False, NativeName: es (ES)" : // MT does not use JS to get the full name
+                    "es-ES: Is Invariant LCID: False, NativeName: espa\u00F1ol (Espa\u00F1a)", output);
 
                 // ignoring the last line of the output which prints the current culture
             }

From 6da6c971c662e716446e8188135bed4498bb7d11 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Fri, 22 Mar 2024 08:03:13 +0000
Subject: [PATCH 08/18] =?UTF-8?q?Assert.Contains=20does=20not=20know=20tha?=
 =?UTF-8?q?t=20`\u00F1`=20is=20same=20as=20`=C3=B1`=20(it=20does=20not=20e?=
 =?UTF-8?q?valuate=20the=20string=20before=20comparison)=20-=20fix=20it=20?=
 =?UTF-8?q?with=20string=20interpolation.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs     | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index 7d43833e119e9..6a8abf9579846 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -69,10 +69,9 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             }
             else
             {
+                string nativeName = IsWorkloadWithMultiThreadingForDefaultFramework ? "es-ES" : "espa\u00F1ol (Espa\u00F1a)"; // MT does not use JS to get the full name
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
-                Assert.Contains(IsWorkloadWithMultiThreadingForDefaultFramework ?
-                    "es-ES: Is Invariant LCID: False, NativeName: es (ES)" : // MT does not use JS to get the full name
-                    "es-ES: Is Invariant LCID: False, NativeName: espa\u00F1ol (Espa\u00F1a)", output);
+                Assert.Contains($"es-ES: Is Invariant LCID: False, NativeName: {nativeName}", output);
 
                 // ignoring the last line of the output which prints the current culture
             }

From 4e8fe6fee51272fde3d009c7b10501e5ca615666 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Fri, 22 Mar 2024 10:16:44 +0000
Subject: [PATCH 09/18] Avoid utf8 signs when using `Assert.Contains`

---
 .../wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs    | 6 +++---
 .../Wasm.Buid.Tests.Programs/InvariantGlobalization.cs      | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index 6a8abf9579846..a1f47fc3f52e5 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -64,14 +64,14 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             if (invariantGlobalization == true)
             {
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
-                Assert.Contains("Could not create es-ES culture", output);
+                Assert.Contains("Could not create de-DE culture", output);
                 Assert.Contains("CurrentCulture.NativeName: Invariant Language (Invariant Country)", output);
             }
             else
             {
-                string nativeName = IsWorkloadWithMultiThreadingForDefaultFramework ? "es-ES" : "espa\u00F1ol (Espa\u00F1a)"; // MT does not use JS to get the full name
+                string nativeName = IsWorkloadWithMultiThreadingForDefaultFramework ? "de-DE" : "Deutsch (Deutschland)"; // MT does not use JS to get the full name
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
-                Assert.Contains($"es-ES: Is Invariant LCID: False, NativeName: {nativeName}", output);
+                Assert.Contains($"de-DE: Is Invariant LCID: False, NativeName: {nativeName}", output);
 
                 // ignoring the last line of the output which prints the current culture
             }
diff --git a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
index 9237110cbc498..593f7d187179f 100644
--- a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
+++ b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
@@ -4,12 +4,12 @@
 // https://github.com/dotnet/runtime/blob/main/docs/design/features/globalization-invariant-mode.md#cultures-and-culture-data
 try
 {
-    CultureInfo culture = new ("es-ES", false);
-    Console.WriteLine($"es-ES: Is Invariant LCID: {culture.LCID == CultureInfo.InvariantCulture.LCID}, NativeName: {culture.NativeName}");
+    CultureInfo culture = new ("de-DE", false);
+    Console.WriteLine($"de-DE: Is Invariant LCID: {culture.LCID == CultureInfo.InvariantCulture.LCID}, NativeName: {culture.NativeName}");
 }
 catch (CultureNotFoundException cnfe)
 {
-    Console.WriteLine($"Could not create es-ES culture: {cnfe.Message}");
+    Console.WriteLine($"Could not create de-DE culture: {cnfe.Message}");
 }
 
 Console.WriteLine($"CurrentCulture.NativeName: {CultureInfo.CurrentCulture.NativeName}");

From 3bfe422f9cee8fc57d3f1447997c98942fd5b3fa Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Fri, 22 Mar 2024 13:12:06 +0000
Subject: [PATCH 10/18] Check exactly what part is not found on helix machine.

---
 src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index a1f47fc3f52e5..a01fdd2b5e354 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -71,7 +71,8 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             {
                 string nativeName = IsWorkloadWithMultiThreadingForDefaultFramework ? "de-DE" : "Deutsch (Deutschland)"; // MT does not use JS to get the full name
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
-                Assert.Contains($"de-DE: Is Invariant LCID: False, NativeName: {nativeName}", output);
+                Assert.Contains("de-DE: Is Invariant LCID: False", output);
+                Assert.Contains($"NativeName: {nativeName}", output);
 
                 // ignoring the last line of the output which prints the current culture
             }

From 2f9b9ecc60ef6e34711194cc8f2083ef4ff3a4d1 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Fri, 22 Mar 2024 16:34:58 +0000
Subject: [PATCH 11/18] `IsWorkloadWithMultiThreadingForDefaultFramework` was
 true even for ST, change to `FEATURE_WASM_MANAGED_THREADS`.

---
 .../wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs   | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index a01fdd2b5e354..16606e6d11da5 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -69,10 +69,13 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             }
             else
             {
-                string nativeName = IsWorkloadWithMultiThreadingForDefaultFramework ? "de-DE" : "Deutsch (Deutschland)"; // MT does not use JS to get the full name
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
                 Assert.Contains("de-DE: Is Invariant LCID: False", output);
-                Assert.Contains($"NativeName: {nativeName}", output);
+#if FEATURE_WASM_MANAGED_THREADS
+                Assert.Contains("NativeName: de-DE", output); // MT does not use JS to get the full name
+#else
+                Assert.Contains("NativeName: Deutsch (Deutschland)", output);
+#endif
 
                 // ignoring the last line of the output which prints the current culture
             }

From 9eeffd4d77d7e7331454ea9f3295e76c39f71a18 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Sat, 23 Mar 2024 07:19:58 +0000
Subject: [PATCH 12/18] Changing locale code was not necessary.

---
 .../wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs  | 8 ++++----
 .../Wasm.Buid.Tests.Programs/InvariantGlobalization.cs    | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index 16606e6d11da5..bd9ccf8434c57 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -64,17 +64,17 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             if (invariantGlobalization == true)
             {
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
-                Assert.Contains("Could not create de-DE culture", output);
+                Assert.Contains("Could not create es-ES culture", output);
                 Assert.Contains("CurrentCulture.NativeName: Invariant Language (Invariant Country)", output);
             }
             else
             {
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
-                Assert.Contains("de-DE: Is Invariant LCID: False", output);
+                Assert.Contains("es-ES: Is Invariant LCID: False", output);
 #if FEATURE_WASM_MANAGED_THREADS
-                Assert.Contains("NativeName: de-DE", output); // MT does not use JS to get the full name
+                Assert.Contains("NativeName: es-ES", output); // MT does not use JS to get the full name
 #else
-                Assert.Contains("NativeName: Deutsch (Deutschland)", output);
+                Assert.Contains("NativeName: espa\u00F1ol (Espa\u00F1a)", output);
 #endif
 
                 // ignoring the last line of the output which prints the current culture
diff --git a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
index 593f7d187179f..10ea73d7398b9 100644
--- a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
+++ b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
@@ -4,12 +4,12 @@
 // https://github.com/dotnet/runtime/blob/main/docs/design/features/globalization-invariant-mode.md#cultures-and-culture-data
 try
 {
-    CultureInfo culture = new ("de-DE", false);
+    CultureInfo culture = new ("es-ES", false);
     Console.WriteLine($"de-DE: Is Invariant LCID: {culture.LCID == CultureInfo.InvariantCulture.LCID}, NativeName: {culture.NativeName}");
 }
 catch (CultureNotFoundException cnfe)
 {
-    Console.WriteLine($"Could not create de-DE culture: {cnfe.Message}");
+    Console.WriteLine($"Could not create es-ES culture: {cnfe.Message}");
 }
 
 Console.WriteLine($"CurrentCulture.NativeName: {CultureInfo.CurrentCulture.NativeName}");

From 1bf5b959407228d098821988befe3d16667db6f8 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Sat, 23 Mar 2024 07:20:55 +0000
Subject: [PATCH 13/18] Fix

---
 .../Wasm.Buid.Tests.Programs/InvariantGlobalization.cs          | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
index 10ea73d7398b9..9237110cbc498 100644
--- a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
+++ b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
@@ -5,7 +5,7 @@
 try
 {
     CultureInfo culture = new ("es-ES", false);
-    Console.WriteLine($"de-DE: Is Invariant LCID: {culture.LCID == CultureInfo.InvariantCulture.LCID}, NativeName: {culture.NativeName}");
+    Console.WriteLine($"es-ES: Is Invariant LCID: {culture.LCID == CultureInfo.InvariantCulture.LCID}, NativeName: {culture.NativeName}");
 }
 catch (CultureNotFoundException cnfe)
 {

From bf5bc9a91be8036410cccf6b03ec020b515e038e Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Mon, 25 Mar 2024 09:07:23 +0000
Subject: [PATCH 14/18] WBT don't run in MT, unless we create a MT app in WBT.

---
 .../wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs     | 4 ++--
 src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs | 4 ----
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs b/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
index 79d3921a9442b..d0957cb54321e 100644
--- a/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
@@ -141,11 +141,11 @@ await BlazorRunTest(new BlazorRunOptions()
         }
         else
         {
-            string nativeName = IsWorkloadWithMultiThreadingForDefaultFramework ? "es-ES" : "espa\u00F1ol (Espa\u00F1a)"; // MT does not use JS to get the full name
             Assert.DoesNotContain("Could not create es-ES culture", output);
             Assert.DoesNotContain("invalid culture", output);
             Assert.DoesNotContain("CurrentCulture.NativeName: Invariant Language (Invariant Country)", output);
-            Assert.Contains($"es-ES: Is-LCID-InvariantCulture: False, NativeName: {nativeName}", output);
+            Assert.Contains("es-ES: Is Invariant LCID: False", output);
+            Assert.Contains("NativeName: espa\u00F1ol (Espa\u00F1a)", output);
 
             // ignoring the last line of the output which prints the current culture
         }
diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index bd9ccf8434c57..911fa85012179 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -71,11 +71,7 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             {
                 string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
                 Assert.Contains("es-ES: Is Invariant LCID: False", output);
-#if FEATURE_WASM_MANAGED_THREADS
-                Assert.Contains("NativeName: es-ES", output); // MT does not use JS to get the full name
-#else
                 Assert.Contains("NativeName: espa\u00F1ol (Espa\u00F1a)", output);
-#endif
 
                 // ignoring the last line of the output which prints the current culture
             }

From 6d34695604fb80d3f7a2930845963454cd0e5216 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Mon, 25 Mar 2024 10:05:19 +0000
Subject: [PATCH 15/18] wrong string

---
 src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs b/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
index d0957cb54321e..a735e2af15e44 100644
--- a/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/Blazor/WorkloadRequiredTests.cs
@@ -144,7 +144,7 @@ await BlazorRunTest(new BlazorRunOptions()
             Assert.DoesNotContain("Could not create es-ES culture", output);
             Assert.DoesNotContain("invalid culture", output);
             Assert.DoesNotContain("CurrentCulture.NativeName: Invariant Language (Invariant Country)", output);
-            Assert.Contains("es-ES: Is Invariant LCID: False", output);
+            Assert.Contains("es-ES: Is-LCID-InvariantCulture: False", output);
             Assert.Contains("NativeName: espa\u00F1ol (Espa\u00F1a)", output);
 
             // ignoring the last line of the output which prints the current culture

From 05d43c713fa6f8d9c9bd53e9f365214cf0296315 Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Mon, 25 Mar 2024 15:01:34 +0000
Subject: [PATCH 16/18] Windows has problems with comparing utf8 by xunit.

---
 .../Wasm.Build.Tests/InvariantGlobalizationTests.cs   |  3 +--
 .../InvariantGlobalization.cs                         | 11 ++++++++++-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
index 911fa85012179..816f088666731 100644
--- a/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
+++ b/src/mono/wasm/Wasm.Build.Tests/InvariantGlobalizationTests.cs
@@ -69,9 +69,8 @@ private void TestInvariantGlobalization(BuildArgs buildArgs, bool? invariantGlob
             }
             else
             {
-                string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id);
+                string output = RunAndTestWasmApp(buildArgs, expectedExitCode: 42, host: host, id: id, args: "nativename=\"espa\u00F1ol (Espa\u00F1a)\"");
                 Assert.Contains("es-ES: Is Invariant LCID: False", output);
-                Assert.Contains("NativeName: espa\u00F1ol (Espa\u00F1a)", output);
 
                 // ignoring the last line of the output which prints the current culture
             }
diff --git a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
index 9237110cbc498..c7b1219b6aabd 100644
--- a/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
+++ b/src/mono/wasm/testassets/Wasm.Buid.Tests.Programs/InvariantGlobalization.cs
@@ -1,11 +1,20 @@
 using System;
 using System.Globalization;
+using System.Linq;
 
 // https://github.com/dotnet/runtime/blob/main/docs/design/features/globalization-invariant-mode.md#cultures-and-culture-data
 try
 {
     CultureInfo culture = new ("es-ES", false);
-    Console.WriteLine($"es-ES: Is Invariant LCID: {culture.LCID == CultureInfo.InvariantCulture.LCID}, NativeName: {culture.NativeName}");
+    Console.WriteLine($"es-ES: Is Invariant LCID: {culture.LCID == CultureInfo.InvariantCulture.LCID}");
+    
+    var nativeNameArg = args.FirstOrDefault(arg => arg.StartsWith("nativename="));
+    if (nativeNameArg == null)
+        throw new ArgumentException($"When not in invariant mode, InvariantGlobalization.cs expects nativename argument with expected es-ES NativeName.");
+    string expectedNativeName = nativeNameArg.Substring(11).Trim('"'); // skip nativename=
+    string nativeName = culture.NativeName;
+    if (nativeName != expectedNativeName)
+        throw new ArgumentException($"Expected es-ES NativeName: {expectedNativeName}, but got: {nativeName}");
 }
 catch (CultureNotFoundException cnfe)
 {

From 697bba874124596259d1fe984d2824835498cbab Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Tue, 26 Mar 2024 08:16:27 +0000
Subject: [PATCH 17/18] Nit: correct comments.

---
 .../src/System/Globalization/CultureData.Browser.cs             | 1 -
 .../System/Globalization/RegionInfoTests.cs                     | 2 +-
 src/mono/browser/runtime/hybrid-globalization/locales.ts        | 2 +-
 3 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
index e8f2927fb4d72..e27de06e5881f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
@@ -25,7 +25,6 @@ private static CultureData JSInitLocaleInfo(string? localeName, CultureData cult
             }
             else
             {
-                // ToDo: make sure we do not re-ask for it
                 // English locale info
                 (culture._sEnglishLanguage, culture._sEnglishCountry) = culture.JSGetLocaleInfo("en-US", localeName);
                 culture._sEnglishDisplayName = string.IsNullOrEmpty(culture._sEnglishCountry) ?
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
index 5783dd62b1997..ee39b219adb3d 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/RegionInfoTests.cs
@@ -136,7 +136,7 @@ public void NativeName(string name, string expected)
             Assert.Equal(expected, new RegionInfo(name).NativeName);
         }
 
-        public static IEnumerable<object[]> EnglishName_TestData() // this might be failing, in that case - fix it or block it
+        public static IEnumerable<object[]> EnglishName_TestData()
         {
             if (SupportFullGlobalizationData)
             {
diff --git a/src/mono/browser/runtime/hybrid-globalization/locales.ts b/src/mono/browser/runtime/hybrid-globalization/locales.ts
index 821ebb3890397..5b7c82a8faa58 100644
--- a/src/mono/browser/runtime/hybrid-globalization/locales.ts
+++ b/src/mono/browser/runtime/hybrid-globalization/locales.ts
@@ -48,7 +48,7 @@ export function mono_wasm_get_locale_info(culture: MonoStringRef, locale: MonoSt
         {
             if (error instanceof RangeError && error.message === "invalid_argument")
             {
-                // it failed from this reason then cultureName is in a form "language-script", without region
+                // if it failed from this reason then cultureName is in a form "language-script", without region
                 try
                 {
                     languageName = new Intl.DisplayNames([cultureName], {type: "language"}).of(localeName);

From 728d82d1a328b53b1dfd6331fe662d75b3ddef4c Mon Sep 17 00:00:00 2001
From: Ilona Tomkowicz <32700855+ilonatommy@users.noreply.github.com>
Date: Tue, 26 Mar 2024 08:50:33 +0000
Subject: [PATCH 18/18] Feedback

---
 .../Globalization/CultureData.Browser.cs      | 32 +++++++++----------
 .../src/System/Globalization/CultureData.cs   |  2 +-
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
index e27de06e5881f..8a8edadaf326d 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.Browser.cs
@@ -12,31 +12,31 @@ internal sealed partial class CultureData
         private const int CULTURE_INFO_BUFFER_LEN = 50;
         private const int LOCALE_INFO_BUFFER_LEN = 80;
 
-        private static CultureData JSInitLocaleInfo(string? localeName, CultureData culture)
+        private void JSInitLocaleInfo()
         {
+            string? localeName = _sName;
             if (string.IsNullOrEmpty(localeName))
             {
-                culture._sEnglishLanguage = "Invariant Language";
-                culture._sNativeLanguage = culture._sEnglishLanguage;
-                culture._sEnglishCountry = "Invariant Country";
-                culture._sNativeCountry = culture._sEnglishCountry;
-                culture._sEnglishDisplayName = $"{culture._sEnglishLanguage} ({culture._sEnglishCountry})";
-                culture._sNativeDisplayName = culture._sEnglishDisplayName;
+                _sEnglishLanguage = "Invariant Language";
+                _sNativeLanguage = _sEnglishLanguage;
+                _sEnglishCountry = "Invariant Country";
+                _sNativeCountry = _sEnglishCountry;
+                _sEnglishDisplayName = $"{_sEnglishLanguage} ({_sEnglishCountry})";
+                _sNativeDisplayName = _sEnglishDisplayName;
             }
             else
             {
                 // English locale info
-                (culture._sEnglishLanguage, culture._sEnglishCountry) = culture.JSGetLocaleInfo("en-US", localeName);
-                culture._sEnglishDisplayName = string.IsNullOrEmpty(culture._sEnglishCountry) ?
-                    culture._sEnglishLanguage :
-                    $"{culture._sEnglishLanguage} ({culture._sEnglishCountry})";
+                (_sEnglishLanguage, _sEnglishCountry) = JSGetLocaleInfo("en-US", localeName);
+                _sEnglishDisplayName = string.IsNullOrEmpty(_sEnglishCountry) ?
+                    _sEnglishLanguage :
+                    $"{_sEnglishLanguage} ({_sEnglishCountry})";
                 // Native locale info
-                (culture._sNativeLanguage, culture._sNativeCountry) = culture.JSGetLocaleInfo(localeName, localeName);
-                culture._sNativeDisplayName = string.IsNullOrEmpty(culture._sNativeCountry) ?
-                    culture._sNativeLanguage :
-                    $"{culture._sNativeLanguage} ({culture._sNativeCountry})";
+                (_sNativeLanguage, _sNativeCountry) = JSGetLocaleInfo(localeName, localeName);
+                _sNativeDisplayName = string.IsNullOrEmpty(_sNativeCountry) ?
+                    _sNativeLanguage :
+                    $"{_sNativeLanguage} ({_sNativeCountry})";
             }
-            return culture;
         }
 
         private unsafe (string, string) JSGetLocaleInfo(string cultureName, string localeName)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
index 47f87734558a1..189ce06de7033 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs
@@ -822,7 +822,7 @@ private static string NormalizeCultureName(string name, out bool isNeutralName)
             {
                 culture = JSLoadCultureInfoFromBrowser(culture._sName, culture);
             }
-            culture = JSInitLocaleInfo(culture._sName, culture);
+            culture.JSInitLocaleInfo();
 #endif
 
             // We need _sWindowsName to be initialized to know if we're using overrides.