How to change locale via URL?

My bilingual Rails 4 application has LocalesController

something like this:

class LocalesController < ApplicationController

  def change_locale
    if params[:set_locale]
      session[:locale] = params[:set_locale] 
      url_hash = Rails.application.routes.recognize_path URI(request.referer).path
      url_hash[:locale] = params[:set_locale]
      redirect_to url_hash



The user can change their language through this form:

def locale_switcher
  form_tag url_for(:controller => 'locales', :action => 'change_locale'), :method => 'get', :id => 'locale_switcher' do
  select_tag 'set_locale', options_for_select(LANGUAGES, I18n.locale.to_s)


It works.

However, right now, the user is unable to change the language via the URL.

eg. if the user is on the page

and then manually changes the url to

, they should see the french version of the page, but nothing happens instead.

This may not matter a lot in many Rails applications, but it does matter in my case.

How can this be fixed?

Thanks for any help.


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3 answers

This is how I did it in one of the Rails 4 applications:

in config / routes.rb:

Rails.application.routes.draw do
  scope "(:locale)", locale: /#{I18n.available_locales.join("|")}/ do
    # rest of your routes here
    # for example:
    resources :projects


make sure that in config / environment / production.rb this line is uncommented:

config.i18n.fallbacks = true


If you want to install default_locale

other than :en

, then in config / application.rb uncomment this line:

config.i18n.default_locale = :de # and then :de will be used as default locale


Now, the last part of your setup, add this method to ApplicationController


class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception

  before_action :set_locale

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

   def default_url_options(options={})
     logger.debug "default_url_options is passed options: #{options.inspect}\n"
     { locale: I18n.locale }


Now to your application, you can access: http://localhost:3000/en/projects

, http://localhost:3000/fr/projects

or http://localhost:3000/projects

. The latter http://localhost:3000/projects

will be used :en

as the default locale (unless you make this change in application.rb).



It might be better to set the locale to routes.rb

like this:

# config/routes.rb
scope "(:locale)", locale: /en|nl/ do
  resources :books


More details here

UPD. If you also keep the locale for the session, you also need to update it on every request. You can set it in a filter as suggested in another answer. But I prefer to use fewer filters:

def locale_for_request
  locale = params[:locale]
  if locale && I18n.locale_available?(locale)
    session[:locale] = locale
    session[:locale] || I18n.default_locale

# then use it in the around filter: I18n.with_locale(locale_for_request)




If you want this behavior, you will have to compare the URL against the session of each request. One way to do this is as follows:

before_filter :check_locale
def check_locale
  if session[:locale] != params[:locale] #I'm assuming this exists in your routes.rb
    params[:set_locale] = params[:locale] #Generally bad to assign things to params but it short for the example




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