diff --git a/lib/processors/manifestCreator.js b/lib/processors/manifestCreator.js
index 948228f69..09f00c27c 100644
--- a/lib/processors/manifestCreator.js
+++ b/lib/processors/manifestCreator.js
@@ -560,9 +560,11 @@ async function createManifest(
 
 		const supportedLocalesArray = Array.from(supportedLocales);
 		supportedLocalesArray.sort();
+
 		return {
 			bundleUrl: i18n,
-			supportedLocales: supportedLocalesArray
+			supportedLocales: supportedLocalesArray,
+			fallbackLocale: supportedLocalesArray.length === 1 ? supportedLocalesArray[0] : undefined
 		};
 	}
 
diff --git a/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/.library b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/.library
index 4ef9fffe7..acfb88eed 100644
--- a/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/.library
+++ b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/.library
@@ -21,7 +21,7 @@
 
 	<appData>
 		<manifest xmlns="http://www.sap.com/ui5/buildext/manifest">
-			<i18n>(i18nPathRelativeToLibrary)</i18n>
+			<i18n>i18nf/custommessagebundle.properties</i18n>
 			<offline>false</offline>
 			<deviceTypes desktop="true" phone="true" tablet="true" />
 			<supportedTheme>sap_belize</supportedTheme>
diff --git a/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/i18nf/custommessagebundle.properties b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/i18nf/custommessagebundle.properties
new file mode 100644
index 000000000..dbb825dab
--- /dev/null
+++ b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/i18nf/custommessagebundle.properties
@@ -0,0 +1 @@
+mytext=Hello
\ No newline at end of file
diff --git a/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/library-preload.js b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/library-preload.js
index 6528441b9..793378555 100644
--- a/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/library-preload.js
+++ b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/library-preload.js
@@ -4,6 +4,6 @@
  */
 sap.ui.predefine("library/i/library", ["sap/ui/core/Core"],function(i){"use strict";sap.ui.getCore().initLibrary({name:"library.i",version:"1.0.0",dependencies:["sap.ui.core"],types:["library.i.ButtonType","library.i.DialogType"],interfaces:["library.i.IContent"],controls:["library.i.Button","library.i.CheckBox","library.i.Dialog","library.i.Input","library.i.Label","library.i.Link","library.i.Menu","library.i.Text"],elements:["library.i.MenuItem"]});return thisLib});
 sap.ui.require.preload({
-	"library/i/manifest.json":'{"_version":"1.21.0","sap.app":{"id":"library.i","type":"library","embeds":[],"i18n":"(i18nPathRelativeToLibrary)","applicationVersion":{"version":"1.0.0"},"title":"{{title}}","description":"{{description}}","ach":"NOT-ME","resources":"resources.json","offline":false,"openSourceComponents":[{"name":"D3.js","packagedWithMySelf":false},{"name":"Hammer.js","packagedWithMySelf":true,"version":"2.0.4"}]},"sap.ui":{"technology":"UI5","deviceTypes":{"desktop":true,"tablet":true,"phone":true},"supportedThemes":[]},"sap.ui5":{"dependencies":{"minUI5Version":"1.0","libs":{"sap.ui.core":{"minVersion":"1.0.0"},"library.d":{"lazy":true}}},"contentDensities":{"cozy":true,"compact":false},"library":{"i18n":false,"content":{"controls":["library.i.Button","library.i.CheckBox","library.i.Dialog","library.i.Input","library.i.Label","library.i.Link","library.i.Menu","library.i.Text"],"elements":["library.i.MenuItem"],"types":["library.i.ButtonType","library.i.DialogType"],"interfaces":["library.i.IContent"]}}},"sap.fiori":{"registrationIds":["F0042"],"archeType":"fancycomponent"}}'
+	"library/i/manifest.json":'{"_version":"1.21.0","sap.app":{"id":"library.i","type":"library","embeds":[],"i18n":{"bundleUrl":"i18nf/custommessagebundle.properties","supportedLocales":[""],"fallbackLocale":""},"applicationVersion":{"version":"1.0.0"},"title":"{{title}}","description":"{{description}}","ach":"NOT-ME","resources":"resources.json","offline":false,"openSourceComponents":[{"name":"D3.js","packagedWithMySelf":false},{"name":"Hammer.js","packagedWithMySelf":true,"version":"2.0.4"}]},"sap.ui":{"technology":"UI5","deviceTypes":{"desktop":true,"tablet":true,"phone":true},"supportedThemes":[]},"sap.ui5":{"dependencies":{"minUI5Version":"1.0","libs":{"sap.ui.core":{"minVersion":"1.0.0"},"library.d":{"lazy":true}}},"contentDensities":{"cozy":true,"compact":false},"library":{"i18n":false,"content":{"controls":["library.i.Button","library.i.CheckBox","library.i.Dialog","library.i.Input","library.i.Label","library.i.Link","library.i.Menu","library.i.Text"],"elements":["library.i.MenuItem"],"types":["library.i.ButtonType","library.i.DialogType"],"interfaces":["library.i.IContent"]}}},"sap.fiori":{"registrationIds":["F0042"],"archeType":"fancycomponent"}}'
 });
 //# sourceMappingURL=library-preload.js.map
diff --git a/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/manifest.json b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/manifest.json
index b10bc0610..0179cfc90 100644
--- a/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/manifest.json
+++ b/test/expected/build/library.i/bundle-library.h-build-manifest/resources/library/i/manifest.json
@@ -4,7 +4,13 @@
     "id": "library.i",
     "type": "library",
     "embeds": [],
-    "i18n": "(i18nPathRelativeToLibrary)",
+    "i18n": {
+      "bundleUrl": "i18nf/custommessagebundle.properties",
+      "supportedLocales": [
+        ""
+      ],
+      "fallbackLocale": ""
+    },
     "applicationVersion": {
       "version": "1.0.0"
     },
diff --git a/test/expected/build/library.i/bundle-library.h/resources/library/i/.library b/test/expected/build/library.i/bundle-library.h/resources/library/i/.library
index 4ef9fffe7..acfb88eed 100644
--- a/test/expected/build/library.i/bundle-library.h/resources/library/i/.library
+++ b/test/expected/build/library.i/bundle-library.h/resources/library/i/.library
@@ -21,7 +21,7 @@
 
 	<appData>
 		<manifest xmlns="http://www.sap.com/ui5/buildext/manifest">
-			<i18n>(i18nPathRelativeToLibrary)</i18n>
+			<i18n>i18nf/custommessagebundle.properties</i18n>
 			<offline>false</offline>
 			<deviceTypes desktop="true" phone="true" tablet="true" />
 			<supportedTheme>sap_belize</supportedTheme>
diff --git a/test/expected/build/library.i/bundle-library.h/resources/library/i/i18nf/custommessagebundle.properties b/test/expected/build/library.i/bundle-library.h/resources/library/i/i18nf/custommessagebundle.properties
new file mode 100644
index 000000000..dbb825dab
--- /dev/null
+++ b/test/expected/build/library.i/bundle-library.h/resources/library/i/i18nf/custommessagebundle.properties
@@ -0,0 +1 @@
+mytext=Hello
\ No newline at end of file
diff --git a/test/expected/build/library.i/bundle-library.h/resources/library/i/manifest.json b/test/expected/build/library.i/bundle-library.h/resources/library/i/manifest.json
index b10bc0610..0179cfc90 100644
--- a/test/expected/build/library.i/bundle-library.h/resources/library/i/manifest.json
+++ b/test/expected/build/library.i/bundle-library.h/resources/library/i/manifest.json
@@ -4,7 +4,13 @@
     "id": "library.i",
     "type": "library",
     "embeds": [],
-    "i18n": "(i18nPathRelativeToLibrary)",
+    "i18n": {
+      "bundleUrl": "i18nf/custommessagebundle.properties",
+      "supportedLocales": [
+        ""
+      ],
+      "fallbackLocale": ""
+    },
     "applicationVersion": {
       "version": "1.0.0"
     },
diff --git a/test/expected/build/library.i/dest/resources/library/i/.library b/test/expected/build/library.i/dest/resources/library/i/.library
index 4ef9fffe7..acfb88eed 100644
--- a/test/expected/build/library.i/dest/resources/library/i/.library
+++ b/test/expected/build/library.i/dest/resources/library/i/.library
@@ -21,7 +21,7 @@
 
 	<appData>
 		<manifest xmlns="http://www.sap.com/ui5/buildext/manifest">
-			<i18n>(i18nPathRelativeToLibrary)</i18n>
+			<i18n>i18nf/custommessagebundle.properties</i18n>
 			<offline>false</offline>
 			<deviceTypes desktop="true" phone="true" tablet="true" />
 			<supportedTheme>sap_belize</supportedTheme>
diff --git a/test/expected/build/library.i/dest/resources/library/i/i18nf/custommessagebundle.properties b/test/expected/build/library.i/dest/resources/library/i/i18nf/custommessagebundle.properties
new file mode 100644
index 000000000..dbb825dab
--- /dev/null
+++ b/test/expected/build/library.i/dest/resources/library/i/i18nf/custommessagebundle.properties
@@ -0,0 +1 @@
+mytext=Hello
\ No newline at end of file
diff --git a/test/expected/build/library.i/dest/resources/library/i/manifest.json b/test/expected/build/library.i/dest/resources/library/i/manifest.json
index 77c819c00..7a3ad6ed7 100644
--- a/test/expected/build/library.i/dest/resources/library/i/manifest.json
+++ b/test/expected/build/library.i/dest/resources/library/i/manifest.json
@@ -4,7 +4,13 @@
     "id": "library.i",
     "type": "library",
     "embeds": [],
-    "i18n": "(i18nPathRelativeToLibrary)",
+    "i18n": {
+      "bundleUrl": "i18nf/custommessagebundle.properties",
+      "supportedLocales": [
+        ""
+      ],
+      "fallbackLocale": ""
+    },
     "applicationVersion": {
       "version": "1.0.0"
     },
diff --git a/test/fixtures/library.i/main/src/library/i/.library b/test/fixtures/library.i/main/src/library/i/.library
index 8c8c09d1b..e035afe77 100644
--- a/test/fixtures/library.i/main/src/library/i/.library
+++ b/test/fixtures/library.i/main/src/library/i/.library
@@ -21,7 +21,7 @@
 
 	<appData>
 		<manifest xmlns="http://www.sap.com/ui5/buildext/manifest">
-			<i18n>(i18nPathRelativeToLibrary)</i18n>
+			<i18n>i18nf/custommessagebundle.properties</i18n>
 			<offline>false</offline>
 			<deviceTypes desktop="true" phone="true" tablet="true" />
 			<supportedTheme>sap_belize</supportedTheme>
diff --git a/test/fixtures/library.i/main/src/library/i/i18nf/custommessagebundle.properties b/test/fixtures/library.i/main/src/library/i/i18nf/custommessagebundle.properties
new file mode 100644
index 000000000..dbb825dab
--- /dev/null
+++ b/test/fixtures/library.i/main/src/library/i/i18nf/custommessagebundle.properties
@@ -0,0 +1 @@
+mytext=Hello
\ No newline at end of file
diff --git a/test/lib/tasks/generateLibraryManifest.js b/test/lib/tasks/generateLibraryManifest.js
index 2df2cab1f..a4a830334 100644
--- a/test/lib/tasks/generateLibraryManifest.js
+++ b/test/lib/tasks/generateLibraryManifest.js
@@ -145,7 +145,8 @@ test("integration: Library with i18n bundle file (messagebundle.properties)", as
 			library: {
 				i18n: {
 					bundleUrl: "messagebundle.properties",
-					supportedLocales: [""]
+					supportedLocales: [""],
+					fallbackLocale: ""
 				}
 			}
 		},
@@ -214,7 +215,154 @@ test("integration: Library with i18n=true declared in .library", async (t) => {
 			library: {
 				i18n: {
 					bundleUrl: "messagebundle.properties",
-					supportedLocales: [""]
+					supportedLocales: [""],
+					fallbackLocale: ""
+				}
+			}
+		},
+	});
+});
+
+test("integration: Library with i18n=true declared in .library and multiple locales", async (t) => {
+	t.context.workspace = createWorkspace();
+
+	t.context.resources = [];
+	t.context.resources.push(createResource({
+		path: "/resources/test/lib/.library",
+		string: `
+			<?xml version="1.0" encoding="UTF-8" ?>
+			<library xmlns="http://www.sap.com/sap.ui.library.xsd" >
+
+				<name>test.lib</name>
+				<vendor>SAP SE</vendor>
+				<copyright></copyright>
+				<version>2.0.0</version>
+
+				<documentation>Test Lib</documentation>
+
+				<appData>
+					<manifest xmlns="http://www.sap.com/ui5/buildext/manifest">
+						<sap.ui5>
+							<library>
+								<i18n>true</i18n>
+							</library>
+						</sap.ui5>
+					</manifest>
+				</appData>
+
+			</library>
+		`,
+		project: t.context.workspace._project
+	}));
+
+	t.context.resources.push(createResource({
+		path: "/resources/test/lib/messagebundle.properties",
+		project: t.context.workspace._project
+	}));
+
+	t.context.resources.push(createResource({
+		path: "/resources/test/lib/messagebundle_en.properties",
+		project: t.context.workspace._project
+	}));
+
+	await assertCreatedManifest(t, {
+		"_version": "1.21.0",
+		"sap.app": {
+			applicationVersion: {
+				version: "2.0.0",
+			},
+			description: "Test Lib",
+			embeds: [],
+			id: "test.lib",
+			offline: true,
+			resources: "resources.json",
+			title: "Test Lib",
+			type: "library",
+		},
+		"sap.ui": {
+			supportedThemes: [],
+			technology: "UI5",
+		},
+		"sap.ui5": {
+			dependencies: {
+				libs: {},
+				minUI5Version: "1.0",
+			},
+			library: {
+				i18n: {
+					bundleUrl: "messagebundle.properties",
+					supportedLocales: ["", "en"]
+				}
+			}
+		},
+	});
+});
+
+test("integration: Library with i18n=true declared in .library and single locale", async (t) => {
+	t.context.workspace = createWorkspace();
+
+	t.context.resources = [];
+	t.context.resources.push(createResource({
+		path: "/resources/test/lib/.library",
+		string: `
+			<?xml version="1.0" encoding="UTF-8" ?>
+			<library xmlns="http://www.sap.com/sap.ui.library.xsd" >
+
+				<name>test.lib</name>
+				<vendor>SAP SE</vendor>
+				<copyright></copyright>
+				<version>2.0.0</version>
+
+				<documentation>Test Lib</documentation>
+
+				<appData>
+					<manifest xmlns="http://www.sap.com/ui5/buildext/manifest">
+						<sap.ui5>
+							<library>
+								<i18n>true</i18n>
+							</library>
+						</sap.ui5>
+					</manifest>
+				</appData>
+
+			</library>
+		`,
+		project: t.context.workspace._project
+	}));
+
+	t.context.resources.push(createResource({
+		path: "/resources/test/lib/messagebundle_de.properties",
+		project: t.context.workspace._project
+	}));
+
+	await assertCreatedManifest(t, {
+		"_version": "1.21.0",
+		"sap.app": {
+			applicationVersion: {
+				version: "2.0.0",
+			},
+			description: "Test Lib",
+			embeds: [],
+			id: "test.lib",
+			offline: true,
+			resources: "resources.json",
+			title: "Test Lib",
+			type: "library",
+		},
+		"sap.ui": {
+			supportedThemes: [],
+			technology: "UI5",
+		},
+		"sap.ui5": {
+			dependencies: {
+				libs: {},
+				minUI5Version: "1.0",
+			},
+			library: {
+				i18n: {
+					bundleUrl: "messagebundle.properties",
+					supportedLocales: ["de"],
+					fallbackLocale: "de"
 				}
 			}
 		},
@@ -345,7 +493,8 @@ test("integration: Library with i18n=foo.properties declared in .library", async
 			library: {
 				i18n: {
 					bundleUrl: "foo.properties",
-					supportedLocales: [""]
+					supportedLocales: [""],
+					fallbackLocale: ""
 				}
 			}
 		},