feat: i18n 개선 및 userfront 로그인/로케일 보완

userfront/test/locale_utils_test.dart

@@ -0,0 +1,66 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:userfront/core/i18n/locale_utils.dart';
+
+void main() {
+  group('locale_utils', () {
+    test('normalizeLocaleCode handles supported locales', () {
+      expect(normalizeLocaleCode('ko'), 'ko');
+      expect(normalizeLocaleCode('ko-KR'), 'ko');
+      expect(normalizeLocaleCode('en'), 'en');
+      expect(normalizeLocaleCode('en-US'), 'en');
+    });
+
+    test('normalizeLocaleCode falls back to default', () {
+      expect(normalizeLocaleCode('ja'), defaultLocaleCode);
+      expect(normalizeLocaleCode(null), defaultLocaleCode);
+      expect(normalizeLocaleCode(''), defaultLocaleCode);
+    });
+
+    test('extractLocaleFromPath picks locale when present', () {
+      expect(extractLocaleFromPath(Uri.parse('/ko/signin')), 'ko');
+      expect(extractLocaleFromPath(Uri.parse('/en/profile')), 'en');
+      expect(extractLocaleFromPath(Uri.parse('/ko')), 'ko');
+    });
+
+    test('extractLocaleFromPath returns null when missing', () {
+      expect(extractLocaleFromPath(Uri.parse('/signin')), isNull);
+      expect(extractLocaleFromPath(Uri.parse('/zz/signin')), isNull);
+    });
+
+    test('stripLocalePath removes locale segment', () {
+      expect(stripLocalePath(Uri.parse('/ko/signin')), '/signin');
+      expect(stripLocalePath(Uri.parse('/en/profile')), '/profile');
+      expect(stripLocalePath(Uri.parse('/ko')), '/');
+      expect(stripLocalePath(Uri.parse('/en/')), '/');
+    });
+
+    test('stripLocalePath keeps path without locale', () {
+      expect(stripLocalePath(Uri.parse('/signin')), '/signin');
+      expect(stripLocalePath(Uri.parse('/auth/callback')), '/auth/callback');
+    });
+
+    test('buildLocalizedPath applies locale', () {
+      expect(buildLocalizedPath('ko', Uri.parse('/signin')), '/ko/signin');
+      expect(buildLocalizedPath('en', Uri.parse('/signin')), '/en/signin');
+      expect(buildLocalizedPath('ko', Uri.parse('/')), '/ko');
+      expect(buildLocalizedPath('en', Uri.parse('/')), '/en');
+    });
+
+    test('buildLocalizedPath preserves query parameters', () {
+      final uri = Uri.parse('/signin?redirect_uri=https://example.com');
+      expect(
+        buildLocalizedPath('ko', uri),
+        '/ko/signin?redirect_uri=https%3A%2F%2Fexample.com',
+      );
+    });
+
+    test('buildLocalizedPath replaces existing locale', () {
+      expect(buildLocalizedPath('en', Uri.parse('/ko/signin')), '/en/signin');
+      expect(buildLocalizedPath('ko', Uri.parse('/en/profile')), '/ko/profile');
+    });
+
+    test('buildLocalizedPath drops unknown 2-letter prefix', () {
+      expect(buildLocalizedPath('ko', Uri.parse('/zz/signin')), '/ko/signin');
+    });
+  });
+}