Rack::ICU4X::Locale

Rack middleware for locale detection using ICU4X. Detects user's preferred locales from various sources (query parameters, cookies, Accept-Language header), with script-safe language negotiation.

Installation

gem 'rack-icu4x-locale'

Requirements

• Ruby 3.2+
• Rack 3.0+

Usage

Basic (Accept-Language header only)

use Rack::ICU4X::Locale, locales: %w[en ja de fr]

run ->(env) {
  locales = env["rack.icu4x.locale"]
  [200, {}, ["Locale: #{locales.first}"]]
}

With Multiple Detectors

use Rack::ICU4X::Locale,
  locales: %w[en ja de fr],
  detectors: [
    {query: "lang"},      # ?lang=ja
    {cookie: "locale"},   # Cookie: locale=ja
    :header               # Accept-Language header
  ],
  default: "en"           # optional: fallback locale when no match

With Custom Detector

use Rack::ICU4X::Locale,
  locales: %w[en ja de fr],
  detectors: [
    ->(env) { env["rack.session"]&.[]("locale") },
    :header
  ]

Detector Types

Type	Example	Description
:header	Accept-Language: ja	Accept-Language header
{cookie: "name"}	Cookie: name=ja	Cookie value
{query: "param"}	?param=ja	Query string parameter
Proc	->(env) { ... }	Custom detection logic

Documentation

See doc/specification.md for detailed specification.

Demo

cd examples
bundle install
bundle exec rackup

Open http://localhost:9292

License

MIT License. See LICENSE.txt.