Add internationalization support with English and French translations

- Introduced a new i18n module for managing translations using JSON files.
- Added English (en.json) and French (fr.json) translation files for UI elements.
- Implemented lazy initialization of the translator to load translations on demand.
- Added unit tests for translation lookup, fallback behavior, and available languages detection.

tests/unit/test_i18n.py

@@ -0,0 +1,60 @@
+"""Unit tests for i18n translation helper."""
+
+import json
+from pathlib import Path
+
+from webdrop_bridge.utils import i18n
+
+
+class TestI18n:
+    """Tests for translation lookup and fallback behavior."""
+
+    def test_tr_lazy_initialization_uses_english_defaults(self):
+        """Translator should lazily initialize and resolve known keys."""
+        # Force a fresh singleton state for this test.
+        i18n._translator = i18n.Translator()  # type: ignore[attr-defined]
+
+        assert i18n.tr("settings.title") == "Settings"
+
+    def test_initialize_with_language_falls_back_to_english(self, tmp_path: Path):
+        """Missing keys in selected language should fall back to English."""
+        translations = tmp_path / "translations"
+        translations.mkdir(parents=True, exist_ok=True)
+
+        (translations / "en.json").write_text(
+            json.dumps(
+                {
+                    "greeting": "Hello {name}",
+                    "settings.title": "Settings",
+                }
+            ),
+            encoding="utf-8",
+        )
+        (translations / "de.json").write_text(
+            json.dumps(
+                {
+                    "settings.title": "Einstellungen",
+                }
+            ),
+            encoding="utf-8",
+        )
+
+        i18n._translator = i18n.Translator()  # type: ignore[attr-defined]
+        i18n.initialize("de", translations)
+
+        assert i18n.tr("settings.title") == "Einstellungen"
+        assert i18n.tr("greeting", name="Alex") == "Hello Alex"
+
+    def test_get_available_languages_reads_translation_files(self, tmp_path: Path):
+        """Available languages should be discovered from JSON files."""
+        translations = tmp_path / "translations"
+        translations.mkdir(parents=True, exist_ok=True)
+        (translations / "en.json").write_text("{}", encoding="utf-8")
+        (translations / "fr.json").write_text("{}", encoding="utf-8")
+
+        i18n._translator = i18n.Translator()  # type: ignore[attr-defined]
+        i18n.initialize("en", translations)
+
+        available = i18n.get_available_languages()
+        assert "en" in available
+        assert "fr" in available