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.

src/webdrop_bridge/config.py

@@ -81,6 +81,7 @@ class Config:
     window_title: str = ""
     enable_logging: bool = True
     enable_checkout: bool = False
+    language: str = "auto"
 
     @classmethod
     def from_file(cls, config_path: Path) -> "Config":
@@ -172,6 +173,7 @@ class Config:
             window_title=window_title,
             enable_logging=data.get("enable_logging", True),
             enable_checkout=data.get("enable_checkout", False),
+            language=data.get("language", "auto"),
         )
 
     @classmethod
@@ -212,6 +214,7 @@ class Config:
         window_title = os.getenv("WINDOW_TITLE", default_title)
         enable_logging = os.getenv("ENABLE_LOGGING", "true").lower() == "true"
         enable_checkout = os.getenv("ENABLE_CHECKOUT", "false").lower() == "true"
+        language = os.getenv("LANGUAGE", "auto")
 
         # Validate log level
         valid_levels = {"DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"}
@@ -304,6 +307,7 @@ class Config:
             window_title=window_title,
             enable_logging=enable_logging,
             enable_checkout=enable_checkout,
+            language=language,
         )
 
     def to_file(self, config_path: Path) -> None:
@@ -332,6 +336,7 @@ class Config:
             "window_title": self.window_title,
             "enable_logging": self.enable_logging,
             "enable_checkout": self.enable_checkout,
+            "language": self.language,
         }
 
         config_path.parent.mkdir(parents=True, exist_ok=True)