Localized url_for let you get your scoped urls auto localized
Example:
All scoped urls on the page http://example.com/en
  will look like:
    - http://example.com/en/contacts
    - http://example.com/en/about
    ...
    
=== Set locale from params:
Add it to ApplicationController

  before_filter :set_locale
  def set_locale
    I18n.locale = params[:locale] unless params[:locale].blank?
  end


=== Config routes:

  scope '(:locale)' do
    #get "/" => 'index#index', :as => 'index'
  end