diff --git a/packages/ckeditor5-alignment/tests/alignmentui.js b/packages/ckeditor5-alignment/tests/alignmentui.js
index ec4011e023f..b470a0af523 100644
--- a/packages/ckeditor5-alignment/tests/alignmentui.js
+++ b/packages/ckeditor5-alignment/tests/alignmentui.js
@@ -303,6 +303,10 @@ describe( 'Alignment UI', () => {
 						content: 'ar',
 						ui: 'ar'
 					},
+					translations: [ { ar: {
+						dictionary: [],
+						getPluralForm: sinon.spy()
+					} } ],
 					plugins: [ AlignmentEditing, AlignmentUI ]
 				} );
 
@@ -437,6 +441,10 @@ describe( 'Alignment UI', () => {
 						language: {
 							content: 'ar'
 						},
+						translations: [ { ar: {
+							dictionary: [],
+							getPluralForm: sinon.spy()
+						} } ],
 						plugins: [ AlignmentEditing, AlignmentUI ],
 						alignment: { options: [ 'center', 'justify' ] }
 					} )
diff --git a/packages/ckeditor5-ckbox/tests/ckboxutils.js b/packages/ckeditor5-ckbox/tests/ckboxutils.js
index 4eda62a6a62..9ce87e22f66 100644
--- a/packages/ckeditor5-ckbox/tests/ckboxutils.js
+++ b/packages/ckeditor5-ckbox/tests/ckboxutils.js
@@ -312,6 +312,10 @@ describe( 'CKBoxUtils', () => {
 		it( 'should set default values', async () => {
 			const editor = await createTestEditor( {
 				language: 'pl',
+				translations: [ { pl: {
+					dictionary: [],
+					getPluralForm: sinon.spy()
+				} } ],
 				cloudServices: {
 					tokenUrl: 'http://cs.example.com'
 				}
diff --git a/packages/ckeditor5-ckfinder/tests/ckfindercommand.js b/packages/ckeditor5-ckfinder/tests/ckfindercommand.js
index c4f4771b4cd..dac2e1958ab 100644
--- a/packages/ckeditor5-ckfinder/tests/ckfindercommand.js
+++ b/packages/ckeditor5-ckfinder/tests/ckfindercommand.js
@@ -260,7 +260,11 @@ describe( 'CKFinderCommand', () => {
 			return VirtualTestEditor
 				.create( {
 					plugins: [ Paragraph, ImageBlockEditing, ImageUploadEditing, LinkEditing, Notification, ClipboardPipeline ],
-					language: 'pl'
+					language: 'pl',
+					translations: [ { pl: {
+						dictionary: [],
+						getPluralForm: sinon.spy()
+					} } ]
 				} )
 				.then( newEditor => {
 					editor = newEditor;
diff --git a/packages/ckeditor5-core/src/context.ts b/packages/ckeditor5-core/src/context.ts
index 1c39c2d264e..8ba6f37cc09 100644
--- a/packages/ckeditor5-core/src/context.ts
+++ b/packages/ckeditor5-core/src/context.ts
@@ -12,6 +12,7 @@ import {
 	Collection,
 	CKEditorError,
 	Locale,
+	global,
 	type LocaleTranslate
 } from '@ckeditor/ckeditor5-utils';
 
@@ -20,6 +21,8 @@ import { type Editor } from './editor/editor.js';
 import type { LoadedPlugins, PluginConstructor } from './plugin.js';
 import type { EditorConfig } from './editor/editorconfig.js';
 
+import { cloneDeep } from 'es-toolkit/compat';
+
 /**
  * Provides a common, higher-level environment for solutions that use multiple {@link module:core/editor/editor~Editor editors}
  * or plugins that work outside the editor. Use it instead of {@link module:core/editor/editor~Editor.create `Editor.create()`}
@@ -160,11 +163,43 @@ export class Context {
 
 		const languageConfig = this.config.get( 'language' ) || {};
 
-		this.locale = new Locale( {
-			uiLanguage: typeof languageConfig === 'string' ? languageConfig : languageConfig.ui,
-			contentLanguage: this.config.get( 'language.content' ),
-			translations
-		} );
+		if ( !translations && global.window.CKEDITOR_TRANSLATIONS ) {
+			/**
+			 * When translations are not provided directly but available via global.window.CKEDITOR_TRANSLATIONS
+			 * (which can be set by CKEditorTranslationsPlugin during manual tests with --language flag,
+			 * or loaded from CDN translation files), we need to ensure the config.language.ui value is properly set.
+			 *
+			 * When translations are loaded via the global variable, the config.language.ui might be missing
+			 * or incorrect, which can cause issues with utilities that depend on the language configuration
+			 * (e.g., date formatting utilities). To fix this, we check if the configured language has matching
+			 * translations, and if not, fall back to the first available language from the global translations object.
+			 *
+			 * Note: The _translate function from translation-service.ts gets translations from
+			 * global.window.CKEDITOR_TRANSLATIONS when translations injected into Locale are empty.
+			 * Since _translate is called often and has no access to the editor config, this is the better place
+			 * to check if translations will be taken from the global variable and update config.language.ui accordingly.
+			 */
+			const globalTranslations = cloneDeep( global.window.CKEDITOR_TRANSLATIONS );
+			const uiLanguageFromConfig = typeof languageConfig === 'string' ? languageConfig : languageConfig.ui;
+			const hasMatchingTranslations = globalTranslations[ uiLanguageFromConfig! ];
+			const defaultGlobalTranslationsLanguage = Object.keys( globalTranslations )[ 0 ];
+
+			this.locale = new Locale( {
+				uiLanguage: hasMatchingTranslations ? uiLanguageFromConfig : defaultGlobalTranslationsLanguage,
+				contentLanguage: this.config.get( 'language.content' ),
+				translations: globalTranslations
+			} );
+
+			if ( !hasMatchingTranslations && this.config.get( 'language.ui' ) !== defaultGlobalTranslationsLanguage ) {
+				this.config.define( 'language.ui', defaultGlobalTranslationsLanguage );
+			}
+		} else {
+			this.locale = new Locale( {
+				uiLanguage: typeof languageConfig === 'string' ? languageConfig : languageConfig.ui,
+				contentLanguage: this.config.get( 'language.content' ),
+				translations
+			} );
+		}
 
 		this.t = this.locale.t;
 
diff --git a/packages/ckeditor5-core/tests/context.js b/packages/ckeditor5-core/tests/context.js
index dd82a04d13d..fe5ec267583 100644
--- a/packages/ckeditor5-core/tests/context.js
+++ b/packages/ckeditor5-core/tests/context.js
@@ -91,26 +91,46 @@ describe( 'Context', () => {
 		} );
 
 		it( 'is configured with the config.language (UI and the content)', () => {
-			const context = new Context( { language: 'pl' } );
+			const context = new Context( { language: 'pl', translations: { pl: {} } } );
 
 			expect( context.locale.uiLanguage ).to.equal( 'pl' );
 			expect( context.locale.contentLanguage ).to.equal( 'pl' );
 		} );
 
 		it( 'is configured with the config.language (different for UI and the content)', () => {
-			const context = new Context( { language: { ui: 'pl', content: 'ar' } } );
+			const context = new Context( { language: { ui: 'pl', content: 'ar' }, translations: { pl: {} } } );
 
 			expect( context.locale.uiLanguage ).to.equal( 'pl' );
 			expect( context.locale.contentLanguage ).to.equal( 'ar' );
 		} );
 
 		it( 'is configured with the config.language (just the content)', () => {
-			const context = new Context( { language: { content: 'ar' } } );
+			const context = new Context( { language: { content: 'ar' }, translations: { pl: {} } } );
 
 			expect( context.locale.uiLanguage ).to.equal( 'en' );
 			expect( context.locale.contentLanguage ).to.equal( 'ar' );
 		} );
 
+		it( 'is configured with the default config.language (when no translations provided)', () => {
+			const context = new Context( { language: 'pl' } );
+
+			expect( context.locale.uiLanguage ).to.equal( 'en' );
+			expect( context.locale.contentLanguage ).to.equal( 'en' );
+		} );
+
+		it( 'is configured with config.language (when no translations provided and dev-translations are matching)', () => {
+			window.CKEDITOR_TRANSLATIONS = {
+				en: { dictionary: {
+					key: ''
+				},
+				getPluralForm: () => '' }
+			};
+			const context = new Context( { language: { ui: 'en', content: 'en' } } );
+
+			expect( context.locale.uiLanguage ).to.equal( 'en' );
+			expect( context.locale.contentLanguage ).to.equal( 'en' );
+		} );
+
 		it( 'is configured with the config.translations', () => {
 			const context = new Context( {
 				translations: {
diff --git a/packages/ckeditor5-core/tests/editor/editor.js b/packages/ckeditor5-core/tests/editor/editor.js
index e6ab49e8e35..7204394690e 100644
--- a/packages/ckeditor5-core/tests/editor/editor.js
+++ b/packages/ckeditor5-core/tests/editor/editor.js
@@ -351,7 +351,13 @@ describe( 'Editor', () => {
 
 		it( 'should use locale instance with a proper configuration passed as the argument to the constructor', () => {
 			const editor = new TestEditor( {
-				language: 'pl'
+				language: 'pl',
+				translations: [ {
+					pl: {
+						dictionary: [],
+						getPluralForm: sinon.spy()
+					}
+				} ]
 			} );
 
 			expect( editor.locale ).to.have.property( 'uiLanguage', 'pl' );
@@ -360,7 +366,13 @@ describe( 'Editor', () => {
 
 		it( 'should use locale instance with a proper configuration set as the defaultConfig option on the constructor', () => {
 			TestEditor.defaultConfig = {
-				language: 'pl'
+				language: 'pl',
+				translations: [ {
+					pl: {
+						dictionary: [],
+						getPluralForm: sinon.spy()
+					}
+				} ]
 			};
 
 			const editor = new TestEditor();
@@ -371,7 +383,13 @@ describe( 'Editor', () => {
 
 		it( 'should prefer the language passed as the argument to the constructor instead of the defaultConfig if both are set', () => {
 			TestEditor.defaultConfig = {
-				language: 'de'
+				language: 'de',
+				translations: [ {
+					pl: {
+						dictionary: [],
+						getPluralForm: sinon.spy()
+					}
+				} ]
 			};
 
 			const editor = new TestEditor( {
@@ -384,10 +402,22 @@ describe( 'Editor', () => {
 
 		it( 'should prefer the language from the context instead of the constructor config or defaultConfig if all are set', async () => {
 			TestEditor.defaultConfig = {
-				language: 'de'
+				language: 'de',
+				translations: [ {
+					pl: {
+						dictionary: [],
+						getPluralForm: sinon.spy()
+					}
+				} ]
 			};
 
-			const context = await Context.create( { language: 'pl' } );
+			const context = await Context.create( {
+				language: 'pl',
+				translations: [ { pl: {
+					dictionary: [],
+					getPluralForm: sinon.spy()
+				} } ]
+			} );
 			const editor = new TestEditor( { context, language: 'ru' } );
 
 			expect( editor.locale ).to.have.property( 'uiLanguage', 'pl' );
diff --git a/packages/ckeditor5-font/tests/ui/colorui.js b/packages/ckeditor5-font/tests/ui/colorui.js
index 987d7930b61..ecc9c3c6e76 100644
--- a/packages/ckeditor5-font/tests/ui/colorui.js
+++ b/packages/ckeditor5-font/tests/ui/colorui.js
@@ -72,7 +72,12 @@ describe( 'FontColorUIBase', () => {
 		return ClassicTestEditor
 			.create( element, {
 				plugins: [ Paragraph, TestColorPlugin, Undo ],
-				testColor: testColorConfig
+				testColor: testColorConfig,
+				language: 'en',
+				translations: [ { en: {
+					dictionary: [],
+					getPluralForm: sinon.spy()
+				} } ]
 			} )
 			.then( newEditor => {
 				editor = newEditor;
diff --git a/packages/ckeditor5-indent/tests/indentui.js b/packages/ckeditor5-indent/tests/indentui.js
index b73e4fa37a5..4dc8909e609 100644
--- a/packages/ckeditor5-indent/tests/indentui.js
+++ b/packages/ckeditor5-indent/tests/indentui.js
@@ -26,7 +26,11 @@ describe( 'IndentUI', () => {
 		rtlEditor = await ClassicTestEditor
 			.create( element, {
 				plugins: [ IndentUI, IndentEditing ],
-				language: 'ar'
+				language: 'ar',
+				translations: [ { ar: {
+					dictionary: [],
+					getPluralForm: sinon.spy()
+				} } ]
 			} );
 	} );
 
diff --git a/packages/ckeditor5-list/tests/legacytodolist/legacytodolistediting.js b/packages/ckeditor5-list/tests/legacytodolist/legacytodolistediting.js
index 27f2d7e8d6d..20f6fe54b3e 100644
--- a/packages/ckeditor5-list/tests/legacytodolist/legacytodolistediting.js
+++ b/packages/ckeditor5-list/tests/legacytodolist/legacytodolistediting.js
@@ -1164,6 +1164,10 @@ describe( 'LegacyTodoListEditing', () => {
 				return VirtualTestEditor
 					.create( {
 						language: 'ar',
+						translations: [ { ar: {
+							dictionary: [],
+							getPluralForm: sinon.spy()
+						} } ],
 						plugins: [ Paragraph, LegacyTodoListEditing, Typing, BoldEditing, BlockQuoteEditing ]
 					} )
 					.then( newEditor => {
diff --git a/packages/ckeditor5-table/tests/tablecellproperties/tablecellpropertiesediting.js b/packages/ckeditor5-table/tests/tablecellproperties/tablecellpropertiesediting.js
index f979638d54c..2a53dc74178 100644
--- a/packages/ckeditor5-table/tests/tablecellproperties/tablecellpropertiesediting.js
+++ b/packages/ckeditor5-table/tests/tablecellproperties/tablecellpropertiesediting.js
@@ -889,7 +889,11 @@ describe( 'table cell properties', () => {
 					beforeEach( async () => {
 						editor = await VirtualTestEditor.create( {
 							plugins: [ TableCellPropertiesEditing, Paragraph, TableEditing ],
-							language: 'ar'
+							language: 'ar',
+							translations: [ { ar: {
+								dictionary: [],
+								getPluralForm: sinon.spy()
+							} } ]
 						} );
 
 						model = editor.model;
diff --git a/packages/ckeditor5-table/tests/tablecolumnresize/tablecolumnresizeediting.js b/packages/ckeditor5-table/tests/tablecolumnresize/tablecolumnresizeediting.js
index 8740a447a94..16a53fcaa17 100644
--- a/packages/ckeditor5-table/tests/tablecolumnresize/tablecolumnresizeediting.js
+++ b/packages/ckeditor5-table/tests/tablecolumnresize/tablecolumnresizeediting.js
@@ -2077,7 +2077,11 @@ describe( 'TableColumnResizeEditing', () => {
 				}
 
 				editor = await createEditor( {
-					language: 'ar'
+					language: 'ar',
+					translations: [ { ar: {
+						dictionary: [],
+						getPluralForm: sinon.spy()
+					} } ]
 				} );
 
 				model = editor.model;
diff --git a/packages/ckeditor5-table/tests/tablekeyboard.js b/packages/ckeditor5-table/tests/tablekeyboard.js
index 5cc04d47731..c2dbaebe331 100644
--- a/packages/ckeditor5-table/tests/tablekeyboard.js
+++ b/packages/ckeditor5-table/tests/tablekeyboard.js
@@ -3602,7 +3602,11 @@ describe( 'TableKeyboard', () => {
 				return VirtualTestEditor
 					.create( {
 						plugins: [ TableEditing, TableKeyboard, TableSelection, Paragraph, ImageBlockEditing, MediaEmbedEditing ],
-						language: 'ar'
+						language: 'ar',
+						translations: [ { ar: {
+							dictionary: [],
+							getPluralForm: sinon.spy()
+						} } ]
 					} )
 					.then( newEditor => {
 						editor = newEditor;
diff --git a/packages/ckeditor5-ui/tests/badge/badge.js b/packages/ckeditor5-ui/tests/badge/badge.js
index a6c69bfcc16..224958300bc 100644
--- a/packages/ckeditor5-ui/tests/badge/badge.js
+++ b/packages/ckeditor5-ui/tests/badge/badge.js
@@ -378,7 +378,11 @@ describe( 'Badge', () => {
 
 		it( 'should position to the left side if the UI language is RTL and no side was configured', async () => {
 			const editor = await createEditor( element, {
-				language: 'ar'
+				language: 'ar',
+				translations: [ { ar: {
+					dictionary: [],
+					getPluralForm: sinon.spy()
+				} } ]
 			} );
 
 			badge = new BadgeExtended( editor );
diff --git a/packages/ckeditor5-ui/tests/editorui/evaluationbadge.js b/packages/ckeditor5-ui/tests/editorui/evaluationbadge.js
index e199831facb..ef6fbb32bc0 100644
--- a/packages/ckeditor5-ui/tests/editorui/evaluationbadge.js
+++ b/packages/ckeditor5-ui/tests/editorui/evaluationbadge.js
@@ -520,7 +520,11 @@ describe( 'EvaluationBadge', () => {
 		it( 'should position the badge to the left right if the UI language is RTL (and powered-by is on the left)', async () => {
 			const editor = await createEditor( element, {
 				language: 'ar',
-				licenseKey: developmentLicenseKey
+				licenseKey: developmentLicenseKey,
+				translations: [ { ar: {
+					dictionary: [],
+					getPluralForm: sinon.spy()
+				} } ]
 			} );
 
 			testUtils.sinon.stub( editor.ui.getEditableElement( 'main' ), 'getBoundingClientRect' ).returns( {
diff --git a/packages/ckeditor5-ui/tests/editorui/poweredby.js b/packages/ckeditor5-ui/tests/editorui/poweredby.js
index 6865d17f1a1..9ba0fa7a80d 100644
--- a/packages/ckeditor5-ui/tests/editorui/poweredby.js
+++ b/packages/ckeditor5-ui/tests/editorui/poweredby.js
@@ -565,7 +565,11 @@ describe( 'PoweredBy', () => {
 
 		it( 'should position the to the left side if the UI language is RTL and no side was configured', async () => {
 			const editor = await createEditor( element, {
-				language: 'ar'
+				language: 'ar',
+				translations: [ { ar: {
+					dictionary: [],
+					getPluralForm: sinon.spy()
+				} } ]
 			} );
 
 			testUtils.sinon.stub( editor.ui.getEditableElement( 'main' ), 'getBoundingClientRect' ).returns( {
diff --git a/packages/ckeditor5-undo/tests/undoui.js b/packages/ckeditor5-undo/tests/undoui.js
index 6f4e412afc1..06293b7875d 100644
--- a/packages/ckeditor5-undo/tests/undoui.js
+++ b/packages/ckeditor5-undo/tests/undoui.js
@@ -21,7 +21,9 @@ describe( 'UndoUI', () => {
 		editorElement = document.createElement( 'div' );
 		document.body.appendChild( editorElement );
 
-		return ClassicTestEditor.create( editorElement, { plugins: [ UndoEditing, UndoUI ] } )
+		return ClassicTestEditor.create( editorElement, { plugins: [ UndoEditing, UndoUI ],
+			language: { ui: 'en' }
+		} )
 			.then( newEditor => {
 				editor = newEditor;
 			} );
@@ -108,7 +110,11 @@ describe( 'UndoUI', () => {
 				return ClassicTestEditor
 					.create( element, {
 						plugins: [ UndoEditing, UndoUI ],
-						language: 'ar'
+						language: 'ar',
+						translations: [ { ar: {
+							dictionary: [],
+							getPluralForm: sinon.spy()
+						} } ]
 					} )
 					.then( newEditor => {
 						const undoButton = newEditor.ui.componentFactory.create( 'undo' );
@@ -129,7 +135,11 @@ describe( 'UndoUI', () => {
 				return ClassicTestEditor
 					.create( element, {
 						plugins: [ UndoEditing, UndoUI ],
-						language: 'ar'
+						language: 'ar',
+						translations: [ { ar: {
+							dictionary: [],
+							getPluralForm: sinon.spy()
+						} } ]
 					} )
 					.then( newEditor => {
 						const redoButton = newEditor.ui.componentFactory.create( 'redo' );