feat: i18n 개선 및 userfront 로그인/로케일 보완

userfront/lib/core/widgets/language_selector.dart

@@ -0,0 +1,65 @@
+import 'package:easy_localization/easy_localization.dart' hide tr;
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+import 'package:userfront/i18n.dart';
+
+import '../i18n/locale_storage.dart';
+import '../i18n/locale_utils.dart';
+
+class LanguageSelector extends StatelessWidget {
+  const LanguageSelector({super.key, this.compact = false});
+
+  final bool compact;
+
+  @override
+  Widget build(BuildContext context) {
+    final current = context.locale.languageCode;
+    final items = [
+      DropdownMenuItem(
+        value: 'ko',
+        child: Text(tr('ui.common.language_ko')),
+      ),
+      DropdownMenuItem(
+        value: 'en',
+        child: Text(tr('ui.common.language_en', fallback: 'English')),
+      ),
+    ];
+
+    final iconSize = compact ? 16.0 : 18.0;
+    final dropdown = DropdownButtonHideUnderline(
+      child: DropdownButton<String>(
+        value: current,
+        items: items,
+        isDense: true,
+        icon: Icon(Icons.arrow_drop_down, size: compact ? 18 : 20),
+        onChanged: (value) async {
+          if (value == null || value == current) {
+            return;
+          }
+          LocaleStorage.write(value);
+          await context.setLocale(Locale(value));
+          final uri = GoRouterState.of(context).uri;
+          final target = buildLocalizedPath(value, uri);
+          if (context.mounted) {
+            context.go(target);
+          }
+        },
+      ),
+    );
+
+    return Padding(
+      padding: EdgeInsets.only(top: compact ? 0 : 2),
+      child: ConstrainedBox(
+        constraints: BoxConstraints(minHeight: compact ? 24 : 28),
+        child: Row(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            Icon(Icons.language, size: iconSize),
+            const SizedBox(width: 6),
+            dropdown,
+          ],
+        ),
+      ),
+    );
+  }
+}