Detailed explanation of the example of I18n for implementing the internationalization of web applications in Python

1. Design concept

The internationalization solution of this project is based on Python's gettext module and provides a flexible and extensible multilingual support system.

2. Language support

2.1 List of supported languages

The project supports over 35 languages, including:

• Chinese (simplified, traditional)
• English
• Hindi language (Hindi, Punjabi, etc.)
• Southeast Asian Languages
• European Languages
• African Languages

2.2 Language code design

Use standard language code formats, such as:

• zh_Hans: Simplified Chinese
• zh_Hant: Traditional Chinese
• en: English

3. Core function analysis

3.1 Get the translator get_translator()

@lru_cache(maxsize=None)
def get_translator(locale: str):
    return (
        'messages',
        localedir=((__file__), 'locales'),
        languages=[locale],
        fallback=True
    )

Use @lru_cache to cache translator instances to improve performance

Load translation files from locales directory

Support language fallback mechanism

3.2 Language Get_locale_from_request()

def get_locale_from_request(request: Request) -> str:
    locale = (
        request.query_params.get('lang') or 
        ('locale') or 
        ('accept-language', 'en')[:2]
    )
    if locale not in SUPPORTED_LANGUAGES:
        locale = 'en'  # Use English by default    return locale

Language acquisition priority:

• URL query parameters
• Cookie
• Browser language header
• Default English

3.3 Middleware i18n_middleware()

def i18n_middleware(get_locale: Callable[[Request], str]):
    async def middleware(request: Request, call_next):
        locale = get_locale(request)
        translator = get_translator(locale)
         = locale
         = 
        .supported_languages = SUPPORTED_LANGUAGES
        response = await call_next(request)
        return response
    return middleware

Middleware functions:

• Set the requested locale
• Inject the translation function gettext
• List of supported languages

4. Use examples

4.1 Used in templates

# In Jinja2 template{{ _('welcome_message') }}

4.2 Used in the code

def some_function(request):
    # Use the translation function in the request    welcome_text = ('welcome_message')

5. Directory structure

locales/
├── en/
│   └── LC_MESSAGES/
│       └──
├── zh_Hans/
│   └── LC_MESSAGES/
│       └──
└── zh_Hant/
    └── LC_MESSAGES/
        └──

6. Performance optimization

Use @lru_cache Cache Translator

Support lazy loading of translation files

Provide language fallback mechanism

7. Best Practices

Using standardized language code

Provides a complete language back-up

Support dynamic language switching

8. Conclusion

This internationalization solution provides a flexible and efficient multilingual support mechanism that can meet the localization needs of complex web applications.

Key technologies:

Python gettext

FastAPI Middleware

LRU cache

Locale detection

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