feat(i18n): add internationalization framework with 10 languages
- Create i18n utility module (app/utils/i18n.py) with translation loading, browser language detection, AI fallback, and l10n helpers - Add JSON translation files for EN, DE, FR, ES, IT, PT, NL, PL, ZH, RU - Add preferred_language column to UserProfile model with migration - Register _() translation function as Jinja2 global - Update base.html with translated navigation, footer, cookie notice - Add language selector dropdown in nav bar (desktop + mobile) - Create API endpoints for language preference (POST/GET /api/i18n/) - Support language detection: user profile > cookie > Accept-Language > default Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
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"""Internationalization (i18n) and localization (l10n) utilities.
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Provides a JSON-based translation system for the DocuElevate UI with:
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* **10 supported languages** (EN, DE, FR, ES, IT, PT, NL, PL, ZH, RU)
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* Browser ``Accept-Language`` detection with cookie & user-profile persistence
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* AI-powered fallback translation via the configured LLM provider
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* Locale-aware date, number, and file-size formatting helpers
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* Jinja2 integration via a ``_()`` global function
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Language resolution order:
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1. User profile ``preferred_language`` (persisted in DB)
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2. ``docuelevate_lang`` cookie
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3. ``Accept-Language`` HTTP header
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4. Default (``en``)
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"""
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from __future__ import annotations
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import json
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import logging
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from datetime import date, datetime
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from functools import lru_cache
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from pathlib import Path
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from typing import Any
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from starlette.requests import Request
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logger = logging.getLogger(__name__)
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# ---------------------------------------------------------------------------
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# Supported languages (ordered by priority)
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# ---------------------------------------------------------------------------
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SUPPORTED_LANGUAGES: list[dict[str, str]] = [
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{"code": "en", "name": "English", "native": "English", "flag": "🇬🇧"},
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{"code": "de", "name": "German", "native": "Deutsch", "flag": "🇩🇪"},
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{"code": "fr", "name": "French", "native": "Français", "flag": "🇫🇷"},
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{"code": "es", "name": "Spanish", "native": "Español", "flag": "🇪🇸"},
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{"code": "it", "name": "Italian", "native": "Italiano", "flag": "🇮🇹"},
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{"code": "pt", "name": "Portuguese", "native": "Português", "flag": "🇵🇹"},
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{"code": "nl", "name": "Dutch", "native": "Nederlands", "flag": "🇳🇱"},
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{"code": "pl", "name": "Polish", "native": "Polski", "flag": "🇵🇱"},
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{"code": "zh", "name": "Chinese", "native": "中文", "flag": "🇨🇳"},
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{"code": "ru", "name": "Russian", "native": "Русский", "flag": "🇷🇺"},
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]
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SUPPORTED_LANGUAGE_CODES: set[str] = {lang["code"] for lang in SUPPORTED_LANGUAGES}
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DEFAULT_LANGUAGE = "en"
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# ---------------------------------------------------------------------------
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# Translation file loading
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# ---------------------------------------------------------------------------
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_TRANSLATIONS_DIR = Path(__file__).resolve().parent.parent.parent / "frontend" / "translations"
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_translation_cache: dict[str, dict[str, str]] = {}
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def _load_translations(locale: str) -> dict[str, str]:
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"""Load the translation JSON file for *locale*, with caching."""
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if locale in _translation_cache:
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return _translation_cache[locale]
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filepath = _TRANSLATIONS_DIR / f"{locale}.json"
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if not filepath.is_file():
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logger.warning("Translation file not found for locale '%s'", locale)
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_translation_cache[locale] = {}
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return {}
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try:
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data: dict[str, str] = json.loads(filepath.read_text(encoding="utf-8"))
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_translation_cache[locale] = data
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return data
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except (json.JSONDecodeError, OSError):
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logger.exception("Failed to load translations for '%s'", locale)
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_translation_cache[locale] = {}
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return {}
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def reload_translations() -> None:
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"""Clear the translation cache so files are re-read on next access."""
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_translation_cache.clear()
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# ---------------------------------------------------------------------------
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# Core translation function
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# ---------------------------------------------------------------------------
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def translate(key: str, locale: str | None = None, **kwargs: Any) -> str:
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"""Return the translated string for *key* in *locale*.
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Falls back through:
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1. Requested *locale*
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2. English (``en``)
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3. The raw key itself (to keep the UI functional)
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Positional placeholders ``{0}``, ``{1}`` or named placeholders
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``{name}`` in the translated string are interpolated via *kwargs*.
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"""
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locale = locale if locale and locale in SUPPORTED_LANGUAGE_CODES else DEFAULT_LANGUAGE
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translations = _load_translations(locale)
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value = translations.get(key)
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# Fallback to English
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if value is None and locale != DEFAULT_LANGUAGE:
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en_translations = _load_translations(DEFAULT_LANGUAGE)
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value = en_translations.get(key)
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# Fallback to key itself
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if value is None:
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value = key
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if kwargs:
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try:
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value = value.format(**kwargs)
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except (KeyError, IndexError):
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pass # Return unformatted string rather than crash
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return value
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# ---------------------------------------------------------------------------
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# AI fallback translation (best-effort, non-blocking)
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# ---------------------------------------------------------------------------
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_ai_translation_cache: dict[tuple[str, str], str] = {}
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def translate_with_ai_fallback(text: str, target_locale: str) -> str:
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"""Translate *text* using the configured AI provider as a fallback.
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Returns the original *text* unchanged when:
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* The target locale is English (source language)
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* The AI provider is unavailable or returns an error
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* The translation has already been cached
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Results are cached in-memory for the lifetime of the process.
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"""
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if target_locale == DEFAULT_LANGUAGE or target_locale not in SUPPORTED_LANGUAGE_CODES:
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return text
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cache_key = (text, target_locale)
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if cache_key in _ai_translation_cache:
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return _ai_translation_cache[cache_key]
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target_name = next(
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(lang["name"] for lang in SUPPORTED_LANGUAGES if lang["code"] == target_locale),
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target_locale,
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)
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try:
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from litellm import completion # type: ignore[import-untyped]
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from app.config import settings
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model = getattr(settings, "ai_model", None) or getattr(settings, "openai_model", "gpt-4o-mini")
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response = completion(
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model=model,
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messages=[
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{
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"role": "system",
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"content": (
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f"You are a professional translator. Translate the following UI text "
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f"from English to {target_name}. Return ONLY the translated text, "
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f"nothing else. Keep any HTML tags, placeholders like {{name}}, "
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f"and special characters intact."
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),
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},
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{"role": "user", "content": text},
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],
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max_tokens=256,
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temperature=0.1,
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)
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translated = response.choices[0].message.content.strip()
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_ai_translation_cache[cache_key] = translated
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return translated
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except Exception:
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logger.debug("AI fallback translation failed for '%s' → %s", text[:50], target_locale)
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return text
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# ---------------------------------------------------------------------------
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# Language detection
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# ---------------------------------------------------------------------------
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def detect_language(request: Request) -> str:
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"""Determine the preferred UI language from the request context.
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Resolution order:
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1. ``preferred_language`` stored in the user session
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2. ``docuelevate_lang`` cookie
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3. ``Accept-Language`` HTTP header (best match)
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4. Default → ``en``
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"""
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# 1. User session preference
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if hasattr(request, "session"):
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session_lang = request.session.get("preferred_language")
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if session_lang and session_lang in SUPPORTED_LANGUAGE_CODES:
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return session_lang
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# 2. Cookie
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cookie_lang = request.cookies.get("docuelevate_lang")
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if cookie_lang and cookie_lang in SUPPORTED_LANGUAGE_CODES:
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return cookie_lang
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# 3. Accept-Language header
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accept = request.headers.get("accept-language", "")
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lang = _parse_accept_language(accept)
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if lang:
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return lang
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return DEFAULT_LANGUAGE
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def _parse_accept_language(header: str) -> str | None:
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"""Extract the best matching language from an ``Accept-Language`` header.
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Parses quality values and returns the highest-priority match among
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:data:`SUPPORTED_LANGUAGE_CODES`, or ``None`` if nothing matches.
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"""
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if not header:
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return None
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entries: list[tuple[float, str]] = []
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for part in header.split(","):
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part = part.strip()
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if not part:
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continue
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if ";q=" in part:
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lang_tag, _, q_str = part.partition(";q=")
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try:
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quality = float(q_str.strip())
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except ValueError:
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quality = 0.0
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else:
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lang_tag = part
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quality = 1.0
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entries.append((quality, lang_tag.strip().lower()))
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# Sort by quality descending
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entries.sort(key=lambda e: e[0], reverse=True)
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for _quality, tag in entries:
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# Try exact match first (e.g., "de", "zh")
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code = tag.split("-")[0]
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if code in SUPPORTED_LANGUAGE_CODES:
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return code
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return None
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# ---------------------------------------------------------------------------
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# Localization helpers (l10n)
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# ---------------------------------------------------------------------------
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# Locale-specific formatting rules for date/number display
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_LOCALE_FORMATS: dict[str, dict[str, Any]] = {
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"en": {
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"date": "%B %d, %Y",
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"date_short": "%m/%d/%Y",
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"datetime": "%B %d, %Y %I:%M %p",
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"thousands_sep": ",",
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"decimal_sep": ".",
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},
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"de": {
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"date": "%d. %B %Y",
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"date_short": "%d.%m.%Y",
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"datetime": "%d. %B %Y %H:%M",
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"thousands_sep": ".",
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"decimal_sep": ",",
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},
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"fr": {
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"date": "%d %B %Y",
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"date_short": "%d/%m/%Y",
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"datetime": "%d %B %Y %H:%M",
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"thousands_sep": "\u202f",
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"decimal_sep": ",",
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},
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"es": {
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"date": "%d de %B de %Y",
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"date_short": "%d/%m/%Y",
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"datetime": "%d de %B de %Y %H:%M",
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"thousands_sep": ".",
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"decimal_sep": ",",
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},
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"it": {
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"date": "%d %B %Y",
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"date_short": "%d/%m/%Y",
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"datetime": "%d %B %Y %H:%M",
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"thousands_sep": ".",
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"decimal_sep": ",",
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},
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"pt": {
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"date": "%d de %B de %Y",
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"date_short": "%d/%m/%Y",
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"datetime": "%d de %B de %Y %H:%M",
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"thousands_sep": ".",
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"decimal_sep": ",",
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},
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"nl": {
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"date": "%d %B %Y",
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"date_short": "%d-%m-%Y",
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"datetime": "%d %B %Y %H:%M",
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"thousands_sep": ".",
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"decimal_sep": ",",
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},
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"pl": {
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"date": "%d %B %Y",
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"date_short": "%d.%m.%Y",
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"datetime": "%d %B %Y %H:%M",
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"thousands_sep": "\u00a0",
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"decimal_sep": ",",
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},
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"zh": {
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"date": "%Y年%m月%d日",
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"date_short": "%Y/%m/%d",
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"datetime": "%Y年%m月%d日 %H:%M",
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"thousands_sep": ",",
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"decimal_sep": ".",
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},
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"ru": {
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"date": "%d %B %Y",
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"date_short": "%d.%m.%Y",
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"datetime": "%d %B %Y %H:%M",
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"thousands_sep": "\u00a0",
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"decimal_sep": ",",
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},
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}
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def format_date(value: date | datetime | None, locale: str = DEFAULT_LANGUAGE, short: bool = False) -> str:
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"""Format a date/datetime value according to the locale conventions."""
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if value is None:
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return ""
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fmt_key = "date_short" if short else "date"
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fmt = _LOCALE_FORMATS.get(locale, _LOCALE_FORMATS[DEFAULT_LANGUAGE])[fmt_key]
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return value.strftime(fmt)
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def format_datetime(value: datetime | None, locale: str = DEFAULT_LANGUAGE) -> str:
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"""Format a datetime value according to the locale conventions."""
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if value is None:
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return ""
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fmt = _LOCALE_FORMATS.get(locale, _LOCALE_FORMATS[DEFAULT_LANGUAGE])["datetime"]
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return value.strftime(fmt)
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def format_number(value: int | float, locale: str = DEFAULT_LANGUAGE) -> str:
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"""Format a number with locale-appropriate thousand separators."""
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lf = _LOCALE_FORMATS.get(locale, _LOCALE_FORMATS[DEFAULT_LANGUAGE])
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if isinstance(value, float):
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int_part, _, dec_part = f"{value:,.2f}".partition(".")
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formatted_int = int_part.replace(",", lf["thousands_sep"])
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return f"{formatted_int}{lf['decimal_sep']}{dec_part}"
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return f"{value:,}".replace(",", lf["thousands_sep"])
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@lru_cache(maxsize=32)
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def get_language_info(code: str) -> dict[str, str] | None:
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"""Return the metadata dict for a supported language code, or ``None``."""
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for lang in SUPPORTED_LANGUAGES:
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if lang["code"] == code:
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return lang
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return None
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