[GR-33683] Update the process of setting the default locale.

PullRequest: graal/10270

docs/reference-manual/native-image/Resources.md

@@ -63,9 +63,9 @@ See also the [guide on assisted configuration of Java resources and other dynami
 ## Locales
 
 It is also possible to specify which locales should be included in the image and what should be the default one.
-For example, to switch the default locale to German and also include French and English, one can use the following hosted options.
+For example, to switch the default locale to Swiss German and also include French and English, one can use the following hosted options.
 ```shell
-native-image -H:DefaultLocale=de -H:IncludeLocales=fr,en
+native-image -Duser.country=CH -Duser.language=de -H:IncludeLocales=fr,en
 ```
 The locales are specified using [language tags](https://docs.oracle.com/javase/tutorial/i18n/locale/matching.html). All
 locales can be included via ``-H:+IncludeAllLocales``, but please note that it increases the size of the resulting

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/jdk/localization/LocalizationFeature.java

@@ -133,9 +133,7 @@ public abstract class LocalizationFeature implements Feature {
     private final ForkJoinPool compressionPool = Options.LocalizationCompressInParallel.getValue() ? new ForkJoinPool(NativeImageOptions.NumberOfThreads.getValue()) : null;
 
     /**
-     * The Locale that the native image is built for. Currently, switching the Locale at run time is
-     * not supported because the resource bundles are only included for one Locale. We use the
-     * Locale that is set for the image generator.
+     * The Locale that the native image is built for.
      */
     protected Locale defaultLocale = Locale.getDefault();
 
@@ -154,7 +152,8 @@ public static class Options {
         @Option(help = "Make all hosted charsets available at run time")//
         public static final HostedOptionKey<Boolean> AddAllCharsets = new HostedOptionKey<>(false);
 
-        @Option(help = "Default locale of the image, by the default it is the same as the default locale of the image builder.", type = OptionType.User)//
+        @Option(help = "Default locale of the image, by the default it is the same as the default locale of the image builder.", type = OptionType.User, //
+                        deprecated = true, deprecationMessage = "Please switch to using system properties such as -Duser.country=CH -Duser.language=de")//
         public static final HostedOptionKey<String> DefaultLocale = new HostedOptionKey<>(Locale.getDefault().toLanguageTag());
 
         @Option(help = "Default charset of the image, by the default it is the same as the default charset of the image builder.", type = OptionType.User)//
@@ -236,8 +235,10 @@ private static ResolvedJavaField findStaticField(ResolvedJavaType declaringClass
     public void afterRegistration(AfterRegistrationAccess access) {
         findClassByName = access::findClassByName;
         allLocales = processLocalesOption();
-        defaultLocale = LocalizationSupport.parseLocaleFromTag(Options.DefaultLocale.getValue());
-        UserError.guarantee(defaultLocale != null, "Invalid default locale %s", Options.DefaultLocale.getValue());
+        if (Options.DefaultLocale.hasBeenSet()) {
+            defaultLocale = LocalizationSupport.parseLocaleFromTag(Options.DefaultLocale.getValue());
+            UserError.guarantee(defaultLocale != null, "Invalid default locale %s", Options.DefaultLocale.getValue());
+        }
         try {
             defaultCharset = Charset.forName(Options.DefaultCharset.getValue());
             VMError.guarantee(defaultCharset.name().equals(Options.DefaultCharset.getValue()),