🌍 Adding Internationalization (i18n) in FastAPI

If you're building a multi-lingual API with FastAPI, it's essential to support internationalization. In this guide, we'll use the python-i18n library — a simple and effective tool for managing translations in Python using JSON files.

📦 Step 1: Install python-i18n

pip install python-i18n

📁 Step 2: Create Locale Files

Create a locales directory and add your language JSON files:

locales/
├── en.json
└── fr.json

en.json:

{
  "greeting": "Hello"
}

fr.json:

{
  "greeting": "Bonjour"
}

⚙️ Step 3: Configure i18n in FastAPI

import i18n
from fastapi import FastAPI, Request

app = FastAPI()

# Load translation files
i18n.load_path.append('locales')
i18n.set('fallback', 'en')

🌐 Step 4: Detect Language from Request

@app.middleware("http")
async def add_language_to_request(request: Request, call_next):
    lang = request.headers.get("Accept-Language", "en").split(",")[0]
    i18n.set("locale", lang)
    response = await call_next(request)
    return response

📨 Step 5: Use Translations in Your API

from fastapi.responses import JSONResponse

@app.get("/greet")
async def greet():
    message = i18n.t("greeting")
    return JSONResponse(content={"message": message})

🔗 Resources

• python-i18n GitHub Repo
• FastAPI Documentation

🎉 Conclusion

With just a few steps, you've added internationalization support to your FastAPI application! Using python-i18n, you can easily expand your app to support more languages and provide localized content.