feat: add support for additional languages in localization

- Expanded the localization support by adding new languages: Chinese (zh), Russian (ru), Dutch (nl), and Spanish (es).
- Updated the localization files and the AppLocalizations class to include the new languages, ensuring a broader reach for international users.
- Enhanced the isSupported method to recognize the newly added languages, improving the app's adaptability to diverse user preferences.

lib/l10n/app_localizations.dart

@@ -7,8 +7,12 @@ import 'package:intl/intl.dart' as intl;
 
 import 'app_localizations_de.dart';
 import 'app_localizations_en.dart';
+import 'app_localizations_es.dart';
 import 'app_localizations_fr.dart';
 import 'app_localizations_it.dart';
+import 'app_localizations_nl.dart';
+import 'app_localizations_ru.dart';
+import 'app_localizations_zh.dart';
 
 // ignore_for_file: type=lint
 
@@ -100,6 +104,10 @@ abstract class AppLocalizations {
     Locale('de'),
     Locale('fr'),
     Locale('it'),
+    Locale('zh'),
+    Locale('ru'),
+    Locale('nl'),
+    Locale('es'),
   ];
 
   /// Application name displayed in the app and OS UI.
@@ -1751,8 +1759,16 @@ class _AppLocalizationsDelegate
   }
 
   @override
-  bool isSupported(Locale locale) =>
-      <String>['de', 'en', 'fr', 'it'].contains(locale.languageCode);
+  bool isSupported(Locale locale) => <String>[
+    'de',
+    'en',
+    'es',
+    'fr',
+    'it',
+    'nl',
+    'ru',
+    'zh',
+  ].contains(locale.languageCode);
 
   @override
   bool shouldReload(_AppLocalizationsDelegate old) => false;
@@ -1765,10 +1781,18 @@ AppLocalizations lookupAppLocalizations(Locale locale) {
       return AppLocalizationsDe();
     case 'en':
       return AppLocalizationsEn();
+    case 'es':
+      return AppLocalizationsEs();
     case 'fr':
       return AppLocalizationsFr();
     case 'it':
       return AppLocalizationsIt();
+    case 'nl':
+      return AppLocalizationsNl();
+    case 'ru':
+      return AppLocalizationsRu();
+    case 'zh':
+      return AppLocalizationsZh();
   }
 
   throw FlutterError(