diff --git a/lib/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart b/lib/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart
index be573c695..0840517a6 100644
--- a/lib/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart
+++ b/lib/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart
@@ -108,6 +108,7 @@ import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions
 import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/handle_create_filter_for_folder.dart';
 import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/handle_preferences_setting_extension.dart';
 import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/handle_save_email_as_draft_extension.dart';
+import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/initialize_app_language.dart';
 import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/open_and_close_composer_extension.dart';
 import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/reopen_composer_cache_extension.dart';
 import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/set_error_extension.dart';
@@ -127,6 +128,7 @@ import 'package:tmail_ui_user/features/manage_account/domain/state/update_vacati
 import 'package:tmail_ui_user/features/manage_account/domain/usecases/create_new_email_rule_filter_interactor.dart';
 import 'package:tmail_ui_user/features/manage_account/domain/usecases/get_all_identities_interactor.dart';
 import 'package:tmail_ui_user/features/manage_account/domain/usecases/get_all_vacation_interactor.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/usecases/save_language_interactor.dart';
 import 'package:tmail_ui_user/features/manage_account/domain/usecases/update_vacation_interactor.dart';
 import 'package:tmail_ui_user/features/manage_account/presentation/extensions/datetime_extension.dart';
 import 'package:tmail_ui_user/features/manage_account/presentation/extensions/vacation_response_extension.dart';
@@ -238,6 +240,7 @@ class MailboxDashBoardController extends ReloadableController
   IOSNotificationManager? _iosNotificationManager;
   GetServerSettingInteractor? getServerSettingInteractor;
   CreateNewEmailRuleFilterInteractor? createNewEmailRuleFilterInteractor;
+  SaveLanguageInteractor? saveLanguageInteractor;
 
   final scaffoldKey = GlobalKey<ScaffoldState>();
   final selectedMailbox = Rxn<PresentationMailbox>();
@@ -465,6 +468,7 @@ class MailboxDashBoardController extends ReloadableController
       );
     } else if (success is GetServerSettingSuccess) {
       isSenderImportantFlagEnabled.value = success.settingOption.isDisplaySenderPriority;
+      initializeAppLanguage(success);
     } else if (success is ClearMailboxSuccess) {
       clearMailboxSuccess(success);
     } else if (success is CreateNewRuleFilterSuccess) {
diff --git a/lib/features/mailbox_dashboard/presentation/extensions/handle_preferences_setting_extension.dart b/lib/features/mailbox_dashboard/presentation/extensions/handle_preferences_setting_extension.dart
index 5719e7145..314fe8655 100644
--- a/lib/features/mailbox_dashboard/presentation/extensions/handle_preferences_setting_extension.dart
+++ b/lib/features/mailbox_dashboard/presentation/extensions/handle_preferences_setting_extension.dart
@@ -1,6 +1,7 @@
 
 import 'package:server_settings/server_settings/capability_server_settings.dart';
 import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/usecases/save_language_interactor.dart';
 import 'package:tmail_ui_user/features/manage_account/presentation/preferences/bindings/preferences_interactors_bindings.dart';
 import 'package:tmail_ui_user/features/server_settings/domain/usecases/get_server_setting_interactor.dart';
 import 'package:tmail_ui_user/main/error/capability_validator.dart';
@@ -21,6 +22,7 @@ extension HandlePreferencesSettingExtension on MailboxDashBoardController {
     if (isServerSettingsCapabilitySupported) {
       PreferencesInteractorsBindings().dependencies();
       getServerSettingInteractor = getBinding<GetServerSettingInteractor>();
+      saveLanguageInteractor = getBinding<SaveLanguageInteractor>();
     }
   }
 
diff --git a/lib/features/mailbox_dashboard/presentation/extensions/initialize_app_language.dart b/lib/features/mailbox_dashboard/presentation/extensions/initialize_app_language.dart
new file mode 100644
index 000000000..e612275f5
--- /dev/null
+++ b/lib/features/mailbox_dashboard/presentation/extensions/initialize_app_language.dart
@@ -0,0 +1,16 @@
+import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart';
+import 'package:tmail_ui_user/features/server_settings/domain/state/get_server_setting_state.dart';
+import 'package:tmail_ui_user/main/localizations/localization_service.dart';
+
+extension InitializeAppLanguage on MailboxDashBoardController {
+  void initializeAppLanguage(GetServerSettingSuccess success) {
+    LocalizationService.initializeAppLanguage(
+      serverLanguage: success.settingOption.language,
+      onServerLanguageApplied: (locale) {
+        if (saveLanguageInteractor != null) {
+          consumeState(saveLanguageInteractor!.execute(locale));
+        }
+      },
+    );
+  }
+}
\ No newline at end of file
diff --git a/lib/features/manage_account/data/datasource/manage_account_datasource.dart b/lib/features/manage_account/data/datasource/preferences_datasource.dart
similarity index 64%
rename from lib/features/manage_account/data/datasource/manage_account_datasource.dart
rename to lib/features/manage_account/data/datasource/preferences_datasource.dart
index a04784535..005048f86 100644
--- a/lib/features/manage_account/data/datasource/manage_account_datasource.dart
+++ b/lib/features/manage_account/data/datasource/preferences_datasource.dart
@@ -1,5 +1,5 @@
 import 'dart:ui';
 
-abstract class ManageAccountDataSource {
+abstract class PreferencesDataSource {
   Future<void> persistLanguage(Locale localeCurrent);
 }
\ No newline at end of file
diff --git a/lib/features/manage_account/data/datasource_impl/manage_account_datasource_impl.dart b/lib/features/manage_account/data/datasource_impl/preferences_datasource_impl.dart
similarity index 82%
rename from lib/features/manage_account/data/datasource_impl/manage_account_datasource_impl.dart
rename to lib/features/manage_account/data/datasource_impl/preferences_datasource_impl.dart
index c9fbdfbb3..74d5a10c4 100644
--- a/lib/features/manage_account/data/datasource_impl/manage_account_datasource_impl.dart
+++ b/lib/features/manage_account/data/datasource_impl/preferences_datasource_impl.dart
@@ -1,15 +1,15 @@
 import 'dart:ui';
 
-import 'package:tmail_ui_user/features/manage_account/data/datasource/manage_account_datasource.dart';
+import 'package:tmail_ui_user/features/manage_account/data/datasource/preferences_datasource.dart';
 import 'package:tmail_ui_user/features/manage_account/data/local/language_cache_manager.dart';
 import 'package:tmail_ui_user/main/exceptions/exception_thrower.dart';
 
-class ManageAccountDataSourceImpl extends ManageAccountDataSource {
+class PreferencesDataSourceImpl extends PreferencesDataSource {
 
   final LanguageCacheManager _languageCacheManager;
   final ExceptionThrower _exceptionThrower;
 
-  ManageAccountDataSourceImpl(
+  PreferencesDataSourceImpl(
     this._languageCacheManager,
     this._exceptionThrower
   );
diff --git a/lib/features/manage_account/data/repository/manage_account_repository_impl.dart b/lib/features/manage_account/data/repository/preferences_repository_impl.dart
similarity index 53%
rename from lib/features/manage_account/data/repository/manage_account_repository_impl.dart
rename to lib/features/manage_account/data/repository/preferences_repository_impl.dart
index d33978915..57914c0d6 100644
--- a/lib/features/manage_account/data/repository/manage_account_repository_impl.dart
+++ b/lib/features/manage_account/data/repository/preferences_repository_impl.dart
@@ -1,13 +1,13 @@
 import 'dart:ui';
 
-import 'package:tmail_ui_user/features/manage_account/data/datasource/manage_account_datasource.dart';
-import 'package:tmail_ui_user/features/manage_account/domain/repository/manage_account_repository.dart';
+import 'package:tmail_ui_user/features/manage_account/data/datasource/preferences_datasource.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/repository/preferences_repository.dart';
 
-class ManageAccountRepositoryImpl extends ManageAccountRepository {
+class PreferencesRepositoryImpl extends PreferencesRepository {
 
-  final ManageAccountDataSource dataSource;
+  final PreferencesDataSource dataSource;
 
-  ManageAccountRepositoryImpl(this.dataSource);
+  PreferencesRepositoryImpl(this.dataSource);
 
   @override
   Future<void> persistLanguage(Locale localeCurrent) {
diff --git a/lib/features/manage_account/domain/repository/manage_account_repository.dart b/lib/features/manage_account/domain/repository/preferences_repository.dart
similarity index 64%
rename from lib/features/manage_account/domain/repository/manage_account_repository.dart
rename to lib/features/manage_account/domain/repository/preferences_repository.dart
index de03d24f4..144c6260f 100644
--- a/lib/features/manage_account/domain/repository/manage_account_repository.dart
+++ b/lib/features/manage_account/domain/repository/preferences_repository.dart
@@ -1,5 +1,5 @@
 import 'dart:ui';
 
-abstract class ManageAccountRepository {
+abstract class PreferencesRepository {
   Future<void> persistLanguage(Locale localeCurrent);
 }
\ No newline at end of file
diff --git a/lib/features/manage_account/domain/usecases/save_language_interactor.dart b/lib/features/manage_account/domain/usecases/save_language_interactor.dart
index c547a09da..2f2cd89c1 100644
--- a/lib/features/manage_account/domain/usecases/save_language_interactor.dart
+++ b/lib/features/manage_account/domain/usecases/save_language_interactor.dart
@@ -4,11 +4,11 @@ import 'dart:ui';
 import 'package:core/presentation/state/failure.dart';
 import 'package:core/presentation/state/success.dart';
 import 'package:dartz/dartz.dart';
-import 'package:tmail_ui_user/features/manage_account/domain/repository/manage_account_repository.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/repository/preferences_repository.dart';
 import 'package:tmail_ui_user/features/manage_account/domain/state/save_language_state.dart';
 
 class SaveLanguageInteractor {
-  final ManageAccountRepository manageAccountRepository;
+  final PreferencesRepository manageAccountRepository;
 
   SaveLanguageInteractor(this.manageAccountRepository);
 
diff --git a/lib/features/manage_account/presentation/language_and_region/language_and_region_bindings.dart b/lib/features/manage_account/presentation/language_and_region/language_and_region_bindings.dart
index d141c1a37..cc58a6889 100644
--- a/lib/features/manage_account/presentation/language_and_region/language_and_region_bindings.dart
+++ b/lib/features/manage_account/presentation/language_and_region/language_and_region_bindings.dart
@@ -1,6 +1,6 @@
 import 'package:get/get.dart';
 import 'package:tmail_ui_user/features/base/base_bindings.dart';
-import 'package:tmail_ui_user/features/manage_account/domain/repository/manage_account_repository.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/repository/preferences_repository.dart';
 import 'package:tmail_ui_user/features/manage_account/domain/usecases/save_language_interactor.dart';
 import 'package:tmail_ui_user/features/manage_account/presentation/language_and_region/language_and_region_controller.dart';
 
@@ -21,7 +21,7 @@ class LanguageAndRegionBindings extends BaseBindings {
 
   @override
   void bindingsInteractor() {
-    Get.lazyPut(() => SaveLanguageInteractor(Get.find<ManageAccountRepository>()));
+    Get.lazyPut(() => SaveLanguageInteractor(Get.find<PreferencesRepository>()));
   }
 
   @override
diff --git a/lib/features/manage_account/presentation/manage_account_dashboard_bindings.dart b/lib/features/manage_account/presentation/manage_account_dashboard_bindings.dart
index a964d8324..bf06fd7b0 100644
--- a/lib/features/manage_account/presentation/manage_account_dashboard_bindings.dart
+++ b/lib/features/manage_account/presentation/manage_account_dashboard_bindings.dart
@@ -1,10 +1,10 @@
 import 'package:get/get.dart';
 import 'package:tmail_ui_user/features/base/base_bindings.dart';
-import 'package:tmail_ui_user/features/manage_account/data/datasource/manage_account_datasource.dart';
-import 'package:tmail_ui_user/features/manage_account/data/datasource_impl/manage_account_datasource_impl.dart';
+import 'package:tmail_ui_user/features/manage_account/data/datasource/preferences_datasource.dart';
+import 'package:tmail_ui_user/features/manage_account/data/datasource_impl/preferences_datasource_impl.dart';
 import 'package:tmail_ui_user/features/manage_account/data/local/language_cache_manager.dart';
-import 'package:tmail_ui_user/features/manage_account/data/repository/manage_account_repository_impl.dart';
-import 'package:tmail_ui_user/features/manage_account/domain/repository/manage_account_repository.dart';
+import 'package:tmail_ui_user/features/manage_account/data/repository/preferences_repository_impl.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/repository/preferences_repository.dart';
 import 'package:tmail_ui_user/features/manage_account/presentation/manage_account_dashboard_controller.dart';
 import 'package:tmail_ui_user/features/manage_account/presentation/menu/manage_account_menu_bindings.dart';
 import 'package:tmail_ui_user/features/manage_account/presentation/menu/settings/settings_bindings.dart';
@@ -28,12 +28,12 @@ class ManageAccountDashBoardBindings extends BaseBindings {
 
   @override
   void bindingsDataSource() {
-    Get.lazyPut<ManageAccountDataSource>(() => Get.find<ManageAccountDataSourceImpl>());
+    Get.lazyPut<PreferencesDataSource>(() => Get.find<PreferencesDataSourceImpl>());
   }
 
   @override
   void bindingsDataSourceImpl() {
-    Get.lazyPut(() => ManageAccountDataSourceImpl(
+    Get.lazyPut(() => PreferencesDataSourceImpl(
       Get.find<LanguageCacheManager>(),
       Get.find<RemoteExceptionThrower>()));
   }
@@ -43,11 +43,11 @@ class ManageAccountDashBoardBindings extends BaseBindings {
 
   @override
   void bindingsRepository() {
-    Get.lazyPut<ManageAccountRepository>(() => Get.find<ManageAccountRepositoryImpl>());
+    Get.lazyPut<PreferencesRepository>(() => Get.find<PreferencesRepositoryImpl>());
   }
 
   @override
   void bindingsRepositoryImpl() {
-    Get.lazyPut(() => ManageAccountRepositoryImpl(Get.find<ManageAccountDataSource>()));
+    Get.lazyPut(() => PreferencesRepositoryImpl(Get.find<PreferencesDataSource>()));
   }
 }
\ No newline at end of file
diff --git a/lib/features/manage_account/presentation/preferences/bindings/preferences_interactors_bindings.dart b/lib/features/manage_account/presentation/preferences/bindings/preferences_interactors_bindings.dart
index 22bab0b44..9e793e6ac 100644
--- a/lib/features/manage_account/presentation/preferences/bindings/preferences_interactors_bindings.dart
+++ b/lib/features/manage_account/presentation/preferences/bindings/preferences_interactors_bindings.dart
@@ -1,5 +1,11 @@
 import 'package:get/get.dart';
 import 'package:tmail_ui_user/features/base/interactors_bindings.dart';
+import 'package:tmail_ui_user/features/manage_account/data/datasource/preferences_datasource.dart';
+import 'package:tmail_ui_user/features/manage_account/data/datasource_impl/preferences_datasource_impl.dart';
+import 'package:tmail_ui_user/features/manage_account/data/local/language_cache_manager.dart';
+import 'package:tmail_ui_user/features/manage_account/data/repository/preferences_repository_impl.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/repository/preferences_repository.dart';
+import 'package:tmail_ui_user/features/manage_account/domain/usecases/save_language_interactor.dart';
 import 'package:tmail_ui_user/features/server_settings/data/datasource/server_settings_data_source.dart';
 import 'package:tmail_ui_user/features/server_settings/data/datasource_impl/remote_server_settings_data_source_impl.dart';
 import 'package:tmail_ui_user/features/server_settings/data/network/server_settings_api.dart';
@@ -7,6 +13,7 @@ import 'package:tmail_ui_user/features/server_settings/data/repository/server_se
 import 'package:tmail_ui_user/features/server_settings/domain/repository/server_settings_repository.dart';
 import 'package:tmail_ui_user/features/server_settings/domain/usecases/get_server_setting_interactor.dart';
 import 'package:tmail_ui_user/features/server_settings/domain/usecases/update_server_setting_interactor.dart';
+import 'package:tmail_ui_user/main/exceptions/cache_exception_thrower.dart';
 import 'package:tmail_ui_user/main/exceptions/remote_exception_thrower.dart';
 
 class PreferencesInteractorsBindings extends InteractorsBindings {
@@ -21,6 +28,10 @@ class PreferencesInteractorsBindings extends InteractorsBindings {
       () => Get.find<RemoteServerSettingsDataSourceImpl>(tag: composerId),
       tag: composerId,
     );
+    Get.lazyPut<PreferencesDataSource>(
+      () => Get.find<PreferencesDataSourceImpl>(tag: composerId),
+      tag: composerId,
+    );
   }
 
   @override
@@ -29,6 +40,10 @@ class PreferencesInteractorsBindings extends InteractorsBindings {
       Get.find<ServerSettingsAPI>(),
       Get.find<RemoteExceptionThrower>(),
     ), tag: composerId);
+    Get.lazyPut(() => PreferencesDataSourceImpl(
+      Get.find<LanguageCacheManager>(),
+      Get.find<CacheExceptionThrower>(),
+    ), tag: composerId);
   }
 
   @override
@@ -41,6 +56,10 @@ class PreferencesInteractorsBindings extends InteractorsBindings {
       () => UpdateServerSettingInteractor(Get.find<ServerSettingsRepository>(tag: composerId)),
       tag: composerId,
     );
+    Get.lazyPut(
+      () => SaveLanguageInteractor(Get.find<PreferencesRepository>(tag: composerId)),
+      tag: composerId,
+    );
   }
 
   @override
@@ -49,6 +68,10 @@ class PreferencesInteractorsBindings extends InteractorsBindings {
       () => Get.find<ServerSettingsRepositoryImpl>(tag: composerId),
       tag: composerId,
     );
+    Get.lazyPut<PreferencesRepository>(
+      () => Get.find<PreferencesRepositoryImpl>(tag: composerId),
+      tag: composerId,
+    );
   }
 
   @override
@@ -57,6 +80,10 @@ class PreferencesInteractorsBindings extends InteractorsBindings {
       () => ServerSettingsRepositoryImpl(Get.find<ServerSettingsDataSource>(tag: composerId)),
       tag: composerId,
     );
+    Get.lazyPut(
+      () => PreferencesRepositoryImpl(Get.find<PreferencesDataSource>(tag: composerId)),
+      tag: composerId,
+    );
   }
 
   void dispose() {
@@ -66,5 +93,11 @@ class PreferencesInteractorsBindings extends InteractorsBindings {
     Get.delete<ServerSettingsRepository>(tag: composerId);
     Get.delete<UpdateServerSettingInteractor>(tag: composerId);
     Get.delete<GetServerSettingInteractor>(tag: composerId);
+    
+    Get.delete<PreferencesDataSourceImpl>(tag: composerId);
+    Get.delete<PreferencesDataSource>(tag: composerId);
+    Get.delete<PreferencesRepositoryImpl>(tag: composerId);
+    Get.delete<PreferencesRepository>(tag: composerId);
+    Get.delete<SaveLanguageInteractor>(tag: composerId);
   }
 }
\ No newline at end of file
diff --git a/lib/main/localizations/localization_service.dart b/lib/main/localizations/localization_service.dart
index 5b4bac3b7..4a8b4f529 100644
--- a/lib/main/localizations/localization_service.dart
+++ b/lib/main/localizations/localization_service.dart
@@ -2,6 +2,7 @@
 import 'dart:ui';
 
 import 'package:core/utils/app_logger.dart';
+import 'package:flutter/widgets.dart';
 import 'package:get/get.dart';
 import 'package:tmail_ui_user/features/manage_account/data/local/language_cache_manager.dart';
 import 'package:tmail_ui_user/main/localizations/language_code_constants.dart';
@@ -45,26 +46,77 @@ class LocalizationService extends Translations {
       log('LocalizationService::_getLocaleFromLanguage:languageCacheManager: $languageCacheManager');
       final localeStored = languageCacheManager?.getStoredLanguage();
       log('LocalizationService::_getLocaleFromLanguage():localeStored: $localeStored');
-      if (localeStored != null) {
-        return localeStored;
-      } else {
-        final languageCodeCurrent = langCode ?? Get.deviceLocale?.languageCode;
-        log('LocalizationService::_getLocaleFromLanguage():languageCodeCurrent: $languageCodeCurrent');
-        final localeSelected = supportedLocales.firstWhereOrNull((locale) => locale.languageCode == languageCodeCurrent);
-        return localeSelected ?? Get.deviceLocale ?? defaultLocale;
-      }
+      final localeSelected = supportedLocales.firstWhereOrNull(
+        (locale) => locale.languageCode == langCode,
+      );
+      return localeSelected ?? localeStored ?? Get.deviceLocale ?? defaultLocale;
     } catch (e) {
       logError('LocalizationService::getLocaleFromLanguage: Exception: $e');
       return Get.deviceLocale ?? defaultLocale;
     }
   }
 
+  static Locale? getCachedLocale() {
+    try {
+      final languageCacheManager = getBinding<LanguageCacheManager>();
+      return languageCacheManager?.getStoredLanguage();
+    } catch (e) {
+      logError('LocalizationService::getCachedLocale: Exception: $e');
+      return null;
+    }
+  }
+
   static String supportedLocalesToLanguageTags() {
     final listLanguageTags = supportedLocales.map((locale) => locale.toLanguageTag()).join(', ');
     log('LocalizationService::supportedLocalesToLanguageTags:listLanguageTags: $listLanguageTags');
     return listLanguageTags;
   }
 
+  static void initializeAppLanguage({
+    String? serverLanguage,
+    void Function(Locale locale)? onServerLanguageApplied,
+  }) {
+    final currentLocale = Get.locale;
+    try {
+      final serverLocale = supportedLocales
+        .firstWhereOrNull((locale) => locale.languageCode == serverLanguage);
+      final cachedLocale = getCachedLocale();
+      
+      // From server
+      if (serverLocale != null && supportedLocales.contains(serverLocale)) {
+        changeLocale(serverLocale.languageCode);
+        onServerLanguageApplied?.call(serverLocale);
+        return;
+      }
+      
+      // From cache
+      if (cachedLocale != null && supportedLocales.contains(cachedLocale)) {
+        changeLocale(cachedLocale.languageCode);
+        return;
+      } 
+      
+      // From device
+      final deviceLocale = WidgetsBinding.instance.platformDispatcher.locale;
+      if (supportedLocales.contains(deviceLocale)) {
+        changeLocale(deviceLocale.languageCode);
+        return;
+      } 
+      
+      // Default
+      if (currentLocale == null || !supportedLocales.contains(currentLocale)) {
+        changeLocale(defaultLocale.languageCode);
+        return;
+      }
+    } catch (e) {
+      logError('LocalizationService::initializeAppLanguage: Exception: $e');
+      // Default
+      if (currentLocale == null || !supportedLocales.contains(currentLocale)) {
+        changeLocale(defaultLocale.languageCode);
+        return;
+      }
+    }
+  }
+
   @override
   Map<String, Map<String, String>> get keys => {};
 }
diff --git a/server_settings/lib/server_settings/tmail_server_settings.dart b/server_settings/lib/server_settings/tmail_server_settings.dart
index 335537dfc..fe339de39 100644
--- a/server_settings/lib/server_settings/tmail_server_settings.dart
+++ b/server_settings/lib/server_settings/tmail_server_settings.dart
@@ -37,9 +37,13 @@ class TMailServerSettingOptions with EquatableMixin {
   @JsonKey(name: 'display.sender.priority')
   final bool? displaySenderPriority;
 
+  @JsonKey(name: 'language')
+  final String? language;
+
   TMailServerSettingOptions({
     this.alwaysReadReceipts,
     this.displaySenderPriority,
+    this.language,
   });
 
   factory TMailServerSettingOptions.fromJson(Map<String, dynamic> json) =>
@@ -50,10 +54,12 @@ class TMailServerSettingOptions with EquatableMixin {
   TMailServerSettingOptions copyWith({
     bool? alwaysReadReceipts,
     bool? displaySenderPriority,
+    String? language,
   }) {
     return TMailServerSettingOptions(
       alwaysReadReceipts: alwaysReadReceipts ?? this.alwaysReadReceipts,
       displaySenderPriority: displaySenderPriority ?? this.displaySenderPriority,
+      language: language ?? this.language,
     );
   }
 
@@ -61,5 +67,6 @@ class TMailServerSettingOptions with EquatableMixin {
   List<Object?> get props => [
     alwaysReadReceipts,
     displaySenderPriority,
+    language,
   ];
 }
diff --git a/test/features/mailbox_dashboard/presentation/extensions/initialize_app_language_test.dart b/test/features/mailbox_dashboard/presentation/extensions/initialize_app_language_test.dart
new file mode 100644
index 000000000..511f6c500
--- /dev/null
+++ b/test/features/mailbox_dashboard/presentation/extensions/initialize_app_language_test.dart
@@ -0,0 +1,315 @@
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:get/get.dart';
+import 'package:mockito/annotations.dart';
+import 'package:mockito/mockito.dart';
+import 'package:server_settings/server_settings/tmail_server_settings.dart';
+import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/controller/mailbox_dashboard_controller.dart';
+import 'package:tmail_ui_user/features/mailbox_dashboard/presentation/extensions/initialize_app_language.dart';
+import 'package:tmail_ui_user/features/manage_account/data/local/language_cache_manager.dart';
+import 'package:tmail_ui_user/features/server_settings/domain/state/get_server_setting_state.dart';
+import 'package:tmail_ui_user/main/localizations/language_code_constants.dart';
+import 'package:tmail_ui_user/main/localizations/localization_service.dart';
+
+import 'initialize_app_language_test.mocks.dart';
+
+@GenerateNiceMocks([
+  MockSpec<MailboxDashBoardController>(),
+  MockSpec<LanguageCacheManager>(),
+])
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  final mailboxDashboardController = MockMailboxDashBoardController();
+  final languageCacheManager = MockLanguageCacheManager();
+
+  setUp(() {
+    Get.testMode = true;
+    Get.locale = const Locale('fr', 'FR');
+    Get.put<LanguageCacheManager>(languageCacheManager);
+  });
+
+  tearDown(() {
+    Get.reset();
+    Get.locale = null;
+    Get.testMode = false;
+    TestWidgetsFlutterBinding.instance.reset();
+  });
+
+  group('initialize app language test:', () {
+    testWidgets(
+      'should apply server language '
+      'when server language is not null '
+      'and server language is supported',
+    (tester) async {
+      // arrange
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: LanguageCodeConstants.vietnamese,
+      ));
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale?.languageCode, LanguageCodeConstants.vietnamese);
+    });
+
+    testWidgets(
+      'should apply cached language '
+      'when server language is null '
+      'and cached language is not null '
+      'and cached language is supported',
+    (tester) async {
+      // arrange
+      const expectedLocale = Locale('en', 'US');
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: null,
+      ));
+      when(languageCacheManager.getStoredLanguage()).thenReturn(expectedLocale);
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, expectedLocale);
+    });
+
+    testWidgets(
+      'should apply cached language '
+      'when server language is not null '
+      'and server language is not supported '
+      'and cached language is not null '
+      'and cached language is supported',
+    (tester) async {
+      // arrange
+      const expectedLocale = Locale('en', 'US');
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: 'fi',
+      ));
+      when(languageCacheManager.getStoredLanguage()).thenReturn(expectedLocale);
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, expectedLocale);
+    });
+
+    testWidgets(
+      'should apply device language '
+      'when server language is null '
+      'and cached language is null '
+      'and device language is supported',
+    (tester) async {
+      // arrange
+      const expectedLocale = Locale('en', 'US');
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: null,
+      ));
+      when(languageCacheManager.getStoredLanguage()).thenReturn(null);
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = expectedLocale;
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, expectedLocale);
+    });
+
+    testWidgets(
+      'should apply device language '
+      'when server language is not null '
+      'and server language is not supported '
+      'and cached language is null '
+      'and device language is supported',
+    (tester) async {
+      // arrange
+      const expectedLocale = Locale('en', 'US');
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: 'fi',
+      ));
+      when(languageCacheManager.getStoredLanguage()).thenReturn(null);
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = expectedLocale;
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, expectedLocale);
+    });
+
+    testWidgets(
+      'should apply device language '
+      'when server language is null '
+      'and cached language is not null '
+      'and cached language is not supported '
+      'and device language is supported',
+    (tester) async {
+      // arrange
+      const expectedLocale = Locale('en', 'US');
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: null,
+      ));
+      when(languageCacheManager.getStoredLanguage())
+        .thenReturn(const Locale('fi', 'FI'));
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = expectedLocale;
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, expectedLocale);
+    });
+
+    testWidgets(
+      'should apply device language '
+      'when server language is not null '
+      'and server language is not supported '
+      'and cached language is not null '
+      'and cached language is not supported '
+      'and device language is supported',
+    (tester) async {
+      // arrange
+      const expectedLocale = Locale('en', 'US');
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: 'es',
+      ));
+      when(languageCacheManager.getStoredLanguage())
+        .thenReturn(const Locale('fi', 'FI'));
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = expectedLocale;
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, expectedLocale);
+    });
+
+    testWidgets(
+      'should apply default language (English) '
+      'when server language is null '
+      'and cached language is null '
+      'and current locale is null '
+      'and device language is not supported',
+    (tester) async {
+      // arrange
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: null,
+      ));
+      when(languageCacheManager.getStoredLanguage()).thenReturn(null);
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = const Locale('es', 'ES');
+      Get.locale = null;
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, LocalizationService.defaultLocale);
+    });
+
+    testWidgets(
+      'should apply default language (English) '
+      'when server language is not null '
+      'and server language is not supported '
+      'and cached language is null '
+      'and current locale is null '
+      'and device language is not supported',
+    (tester) async {
+      // arrange
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: 'fi',
+      ));
+      when(languageCacheManager.getStoredLanguage()).thenReturn(null);
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = const Locale('es', 'ES');
+      Get.locale = null;
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, LocalizationService.defaultLocale);
+    });
+
+    testWidgets(
+      'should apply default language (English) '
+      'when server language is null '
+      'and cached language is not null '
+      'and cached language is not supported '
+      'and current locale is null '
+      'and device language is not supported',
+    (tester) async {
+      // arrange
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: null,
+      ));
+      when(languageCacheManager.getStoredLanguage())
+        .thenReturn(const Locale('fi', 'FI'));
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = const Locale('es', 'ES');
+      Get.locale = null;
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, LocalizationService.defaultLocale);
+    });
+
+    testWidgets(
+      'should apply default language (English) '
+      'when server language is null '
+      'and cached language is null '
+      'and current locale is not null '
+      'and current locale is not supported '
+      'and device language is not supported',
+    (tester) async {
+      // arrange
+      final success = GetServerSettingSuccess(TMailServerSettingOptions(
+        language: null,
+      ));
+      when(languageCacheManager.getStoredLanguage()).thenReturn(null);
+      TestWidgetsFlutterBinding
+        .instance
+        .platformDispatcher
+        .localeTestValue = const Locale('es', 'ES');
+      Get.locale = const Locale('fi', 'FI');
+      
+      // act
+      mailboxDashboardController.initializeAppLanguage(success);
+      await tester.pumpAndSettle();
+      
+      // assert
+      expect(Get.locale, LocalizationService.defaultLocale);
+    });
+  });
+}
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