feat(localization): Implement Swedish localization and error messages

- Added localization support for Swedish and English languages.
- Integrated localized strings for user messages in the API error mapper.
- Updated UI components to use localized strings for labels and messages.
- Ensured all error messages are context-aware and utilize the localization framework.
- Created regression test to prevent common ASCII fallbacks in Swedish UI text.

flutter/lib/core/l10n/l10n.dart

@@ -0,0 +1,6 @@
+import 'package:flutter/widgets.dart';
+import 'package:flutter_gen/gen_l10n/app_localizations.dart';
+
+extension AppLocalizationsX on BuildContext {
+  AppLocalizations get l10n => AppLocalizations.of(this)!;
+}