Setting locale in ApplicationController

application_controller.rb

# encoding: utf-8

class ApplicationController < ActionController::Base
  protect_from_forgery
  before_filter :set_locale

  private

  def set_locale
    I18n.locale = params[:locale] ||
                  session[:locale] ||
                  extract_locale_from_host ||
                  extract_locale_from_accept_language_header ||
                  I18n.default_locale
  end

  def extract_locale_from_accept_language_header
    unless request.env['HTTP_ACCEPT_LANGUAGE'].nil?
      request.env['HTTP_ACCEPT_LANGUAGE'].scan(/^[a-z]{2}/).first
    end
  end 

  def extract_locale_from_host
    case request.host
      when /cn/
        I18n.locale = :zh
    end
  end

end

application_controller_spec.rb

require 'spec_helper'

describe ApplicationController do

  controller do
    def index
      render :text => "Success!"
    end
  end

  describe "extracting locale from browser language" do
    it "sets locale to english" do
      get :index
      expect(I18n.locale).to eq(:en)
    end
    it "sets locale to english" do
      request.env['HTTP_ACCEPT_LANGUAGE'] = 'en-us'
      get :index
      expect(I18n.locale).to eq(:en)
    end
    it "sets locale to chinese" do
      request.env['HTTP_ACCEPT_LANGUAGE'] = 'zh-cn'
      get :index
      expect(I18n.locale).to eq(:zh)
    end
  end

  describe "extracting locale from host" do
    it "sets the locale to english" do
      request.env['HTTP_HOST'] = 'www.durst.org'
      get :index
      expect(I18n.locale).to eq(:en)
    end
    it "sets the locale to chinese" do
      request.env['HTTP_HOST'] = 'www.durst.cn.com'
      get :index
      expect(I18n.locale).to eq(:zh)
    end
    it "sets the locale to chinese" do
      request.env['HTTP_HOST'] = 'www.durst.net.cn'
      get :index
      expect(I18n.locale).to eq(:zh)
    end
  end

  describe "extracting locale from param" do
    it "sets the locale to chinese" do
      get :index, {:locale => "zh"}
      expect(I18n.locale).to eq(:zh)
    end
  end

  describe "extracting locale from session" do
    it "sets the locale to chinese" do
      session[:locale] = :zh
      get :index
      expect(I18n.locale).to eq(:zh)
    end
  end


end