i18n-fastapi 0.1.3

High-performance i18n for FastAPI with Rust-powered translation engine

i18n-fastapi

High-performance internationalization for FastAPI, powered by a Rust translation engine with automatic Python fallback.

Features

• Rust-powered engine — blazing-fast translation lookups via PyO3, with pure Python fallback
• ICU plural support — zero / one / two / few / many / other
• Configurable locale detection — query params, cookies, headers, path prefix, in any priority order
• Plugin pattern — one-line setup with I18n(app)
• Multiple locale directories — shared + per-module translations with filename-based namespacing
• Duplicate key detection — catch conflicts at startup, not at runtime
• Hot reload — watch translation files during development
• Built-in endpoint — GET /i18n/languages returns available locales
• FastAPI dependencies — inject Locale and TranslateFunc into route handlers

Installation

pip install i18n-fastapi

For hot reload during development:

pip install "i18n-fastapi[reload]"

Quick Start

Create translation files:

locales/
├── en/
│   └── messages.json    # {"greeting": "Hello {name}"}
└── es/
    └── messages.json    # {"greeting": "Hola {name}"}

Set up your app:

from fastapi import FastAPI
from i18n_fastapi import I18n, t

app = FastAPI()
I18n(app)

@app.get("/greet")
async def greet():
    return {"message": t("messages.greeting", name="World")}

Request with ?lang=es or Accept-Language: es and the response adapts automatically.

Documentation

• Usage Guide — configuration, locale detection, pluralization, and more
• Contributing — how to set up the dev environment, run tests, and submit PRs
• Publishing — how to publish releases to PyPI
• Changelog — version history
• Code of Conduct — community standards

Author

Johnatan Palacios Londoño — [e-mail]

License

MIT