fix: remove unsupported languages from language picker

Remove languages from _getLanguageName that don't have >90% translation
coverage and aren't in appSupportedLocales (Finnish, Korean, Arabic).
Also improve Chinese locale display.

- Removed fi, ko, ar cases that don't meet translation threshold
- Fixed Chinese locale handling to properly show "中文 (简体)" for zh_CN
- Ensures only properly translated languages appear in the picker

Co-authored-by: Claude <noreply@anthropic.com>

mobile/apps/photos/lib/ui/settings/language_picker.dart

@@ -159,16 +159,11 @@ class _ItemsWidgetState extends State<ItemsWidget> {
         return 'Русский';
       case 'tr':
         return 'Türkçe';
-      case 'fi':
-        return 'Suomi';
       case 'zh':
+        if (locale.countryCode == 'CN') {
+          return '中文 (简体)';
+        }
         return '中文';
-      case 'zh-CN':
-        return '中文';
-      case 'ko':
-        return '한국어';
-      case 'ar':
-        return 'العربية';
       case 'uk':
         return 'Українська';
       case 'vi':