How to set locale on Rails with cookies

set_locale.rb

class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception
  before_action :set_locale

  private
    # Before every request, we set the locale, from the specified or detected settings, or from the cookie
    def set_locale
      if language_change_necessary?
        I18n.locale = the_new_locale
        set_locale_cookie(I18n.locale)

        if params.has_key?(:locale)
          redirect_to(url_for(params.permit(:locale).except(:locale)))
        end
      else
        use_locale_from_cookie
      end
    end

    # A locale change is necessary if no locale cookie is found, or if the locale param has been specified
    def language_change_necessary?
      return cookies['locale'].nil? || params[:locale]
    end

    # The new locale is taken from the current_user language setting, it logged_in, or from the http accept language header if not
    # In both cases, if a locale param has been passed, it takes precedence. Only available locales are accepted
    def the_new_locale
      new_locale = (params[:locale] || extract_locale_from_accept_language_header)
      ['en', 'ru'].include?(new_locale) ? new_locale : I18n.default_locale.to_s
    end

    # Sets the locale cookie
    def set_locale_cookie(locale)
      cookies['locale'] = locale.to_s
    end

    # Reads the locale cookie and sets the locale from it
    def use_locale_from_cookie
      if cookies['locale']
        I18n.locale = cookies['locale']
      end
    end

    # Extracts the locale from the accept language header, if found
    def extract_locale_from_accept_language_header
      # locale = request.env['HTTP_ACCEPT_LANGUAGE'].scan(/^[a-z]{2}/).first rescue I18n.default_locale
      I18n.default_locale
    end
end