feat(i18n): add backend translation utility with shared locale files

backend/app/utils/__init__.py

@@ -4,6 +4,7 @@
 
 from .file_parser import FileParser
 from .llm_client import LLMClient
+from .locale import t, get_locale, get_language_instruction
 
-__all__ = ['FileParser', 'LLMClient']
+__all__ = ['FileParser', 'LLMClient', 't', 'get_locale', 'get_language_instruction']
 

backend/app/utils/locale.py

@@ -0,0 +1,60 @@
+import json
+import os
+from flask import request, has_request_context
+
+_locales_dir = os.path.join(os.path.dirname(__file__), '..', '..', '..', 'locales')
+
+# Load language registry
+with open(os.path.join(_locales_dir, 'languages.json'), 'r', encoding='utf-8') as f:
+    _languages = json.load(f)
+
+# Load translation files
+_translations = {}
+for filename in os.listdir(_locales_dir):
+    if filename.endswith('.json') and filename != 'languages.json':
+        locale_name = filename[:-5]
+        with open(os.path.join(_locales_dir, filename), 'r', encoding='utf-8') as f:
+            _translations[locale_name] = json.load(f)
+
+
+def get_locale() -> str:
+    if has_request_context():
+        return request.headers.get('Accept-Language', 'zh')
+    return 'zh'
+
+
+def t(key: str, **kwargs) -> str:
+    locale = get_locale()
+    messages = _translations.get(locale, _translations.get('zh', {}))
+
+    value = messages
+    for part in key.split('.'):
+        if isinstance(value, dict):
+            value = value.get(part)
+        else:
+            value = None
+            break
+
+    if value is None:
+        value = _translations.get('zh', {})
+        for part in key.split('.'):
+            if isinstance(value, dict):
+                value = value.get(part)
+            else:
+                value = None
+                break
+
+    if value is None:
+        return key
+
+    if kwargs:
+        for k, v in kwargs.items():
+            value = value.replace(f'{{{k}}}', str(v))
+
+    return value
+
+
+def get_language_instruction() -> str:
+    locale = get_locale()
+    lang_config = _languages.get(locale, _languages.get('zh', {}))
+    return lang_config.get('llmInstruction', '请使用中文回答。')