A really small library to translate routes for better SEO

route_translator.rb

class RouteTranslator

  def self.routes(rails_router, &block)
     RouteTranslator.new(rails_router).instance_eval(&block)
  end

  def initialize(rails_router)
    @rails_router = rails_router
  end

  def get(route, options)
    redirect = options.key?(:redirect) ? options[:redirect] : true
    options.delete(:redirect)

    I18n.available_locales.each do |loc|
      rails_router.scope loc, defaults: { locale: loc } do
        rails_router.get(translate_route(route, loc), options.merge(as: "#{options[:as] || route}_#{loc}"))
      end
    end

    return unless redirect
    I18n.available_locales.each do |loc|
      translated = translate_route(route, loc)
      rails_router.get(translated, to: rails_router.redirect("#{loc}/#{translated}"))
    end
  end

  private

    attr_reader :rails_router

    def translate_route(route, locale)
      path = "routes.#{route}"
      unless I18n.exists?(path, locale)
        fail "you need to define '#{locale}::routes::#{route}' in your 'routes.yml'"
      end
      I18n.t(path, locale: locale)
    end
end

Acording to SEO best practices you should translate the URLs for multilingual sites. To do that in rails you have to add a lot of lines to your routes.rb. For example if you have prices and questions in two languages you'd have something like this:

# routes.rb
get 'questions', to: redirect('en/questions')
get 'prices', to: redirect('en/prices')

scope :en, defaults: { locale: :es } do
  get 'questions', to: 'home#questions', as: :questions_en
  get 'prices', to: 'home#prices', as: :prices_en
end

get 'preguntas', to: redirect('es/preguntas')
get 'precios', to: redirect('es/precios')

scope :es, defaults: { locale: :es } do
  get 'preguntas', to: 'home#questions', as: :questions_es
  get 'precios', to: 'home#prices', as: :prices_es
end 

The redirect is for users langing in /prices to be redirect to /en/prices

This library allows you to do the exact same thing with 4 lines of code in your routes.rb and some in your config/locales folder:

# routes.rb
LanguageRoutes.routes(self) do
  get :questions, to: 'home#questions'
  get :prices, to: 'home#prices'
end

# config/locales/routes.yml
en:
  routes:
    questions: questions
    prices: prices
es:
  routes:
    questions: preguntas
    prices: precios

Which will generate:

   questions_es GET  /es/preguntas(.:format)   home#questions {:locale=>:es}
   questions_en GET  /en/questions(.:format)   home#questions {:locale=>:en}
      preguntas GET  /preguntas(.:format)      redirect(301, es/preguntas)
      questions GET  /questions(.:format)      redirect(301, en/questions)
      prices_es GET  /es/precios(.:format)     home#prices {:locale=>:es}
      prices_en GET  /en/prices(.:format)      home#prices {:locale=>:en}
        precios GET  /precios(.:format)        redirect(301, es/precios)
         prices GET  /prices(.:format)         redirect(301, en/prices)

That's it