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/test/core/swedish_strings_regression_test.dart

@@ -0,0 +1,47 @@
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  test('Flutter lib should not contain common ASCII fallbacks for Swedish UI text', () {
+    const forbiddenSpellings = <String, String>{
+      'Forsok': 'Försök',
+      'gatt ut': 'gått ut',
+      'behorighet': 'behörighet',
+      'Natverksfel': 'Nätverksfel',
+      'ovantat': 'oväntat',
+      'Lagg': 'Lägg',
+      'Valj': 'Välj',
+      'Mangd': 'Mängd',
+      'Oppnad': 'Öppnad',
+      'Bast fore': 'Bäst före',
+      'Inkop': 'Inköp',
+      'Ovrigt': 'Övrigt',
+      'Okant': 'Okänt',
+      'hamta': 'hämta',
+      'tillgangligt': 'tillgängligt',
+      'raknar': 'räknar',
+    };
+
+    final offenders = <String>[];
+    final files = Directory('lib')
+        .listSync(recursive: true)
+        .whereType<File>()
+        .where((file) => file.path.endsWith('.dart'));
+
+    for (final file in files) {
+      final content = file.readAsStringSync();
+      for (final entry in forbiddenSpellings.entries) {
+        if (content.contains(entry.key)) {
+          offenders.add('${file.path}: found "${entry.key}"; use "${entry.value}"');
+        }
+      }
+    }
+
+    expect(
+      offenders,
+      isEmpty,
+      reason: offenders.isEmpty ? null : offenders.join('\n'),
+    );
+  });
+}