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locales/i18n.py

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+"""
+i18n (Internationalization) module for AI Novel Generator.
+Loads locale-specific JSON files and provides a simple t(key) function to retrieve translated strings.
+
+Usage:
+    from locales.i18n import t, set_language
+
+    set_language("VI")  # Switch to Vietnamese
+    print(t("app.title"))  # Prints Vietnamese title
+
+Language can also be set via environment variable APP_LANGUAGE (default: "VI").
+"""
+
+import json
+import os
+import logging
+
+logger = logging.getLogger("i18n")
+
+# Global state
+_current_language = None
+_translations = {}
+_locales_dir = os.path.dirname(os.path.abspath(__file__))
+
+
+def load_locale(lang: str) -> dict:
+    """Load a locale JSON file and return the translations dict."""
+    locale_path = os.path.join(_locales_dir, lang, "messages.json")
+    if not os.path.exists(locale_path):
+        logger.error(f"Locale file not found: {locale_path}")
+        return {}
+
+    try:
+        with open(locale_path, "r", encoding="utf-8") as f:
+            return json.load(f)
+    except (json.JSONDecodeError, IOError) as e:
+        logger.error(f"Failed to load locale '{lang}': {e}")
+        return {}
+
+
+def set_language(lang: str) -> None:
+    """Set the active language and load its translations."""
+    global _current_language, _translations
+    _current_language = lang
+    _translations = load_locale(lang)
+    if _translations:
+        logger.info(f"Language set to: {lang}")
+    else:
+        logger.warning(f"No translations loaded for language: {lang}")
+
+
+def get_language() -> str:
+    """Return the current language code."""
+    return _current_language or "VI"
+
+
+def t(key: str, **kwargs) -> str:
+    """
+    Translate a dot-notation key to the localized string.
+
+    Args:
+        key: Dot-separated key path, e.g. "tabs.rewrite" or "messages.polish_success"
+        **kwargs: Optional format parameters to interpolate into the string.
+
+    Returns:
+        The translated string, or the key itself if not found (for debugging).
+    """
+    global _translations
+
+    # Auto-initialize if not yet loaded
+    if not _translations:
+        init_lang = os.getenv("APP_LANGUAGE", "VI")
+        set_language(init_lang)
+
+    # Traverse the nested dict
+    parts = key.split(".")
+    value = _translations
+    for part in parts:
+        if isinstance(value, dict) and part in value:
+            value = value[part]
+        else:
+            logger.warning(f"Missing translation key: '{key}' (language: {_current_language})")
+            return key  # Return the key itself as fallback
+
+    if isinstance(value, str):
+        if kwargs:
+            try:
+                return value.format(**kwargs)
+            except KeyError:
+                return value
+        return value
+
+    # If value is a list (e.g. dropdown choices), return it directly
+    if isinstance(value, list):
+        return value
+
+    # If value is still a dict, return the key
+    logger.warning(f"Translation key '{key}' resolved to a dict, not a string")
+    return key
+
+
+# Auto-initialize on import
+_init_lang = os.getenv("APP_LANGUAGE", "VI")
+set_language(_init_lang)