heroku - rails 4 locale switcher not working on heroku

Question

I have a bilingual rails 4 application deployed in Heroku - russian & english. Everything worked until one day the locale switcher broke for no reason. It's working completely fine on development and production version - when I point to language link it shows the normal link with 'localhost:3000/en' or 'localhost:3000/ru' param. But in Heroku it shows 'abarskaya.com/%7B:locale=>' instead of 'abarskaya.com/ru' or 'abarskaya.com/en'. This is really strange as I didn't change anything. Here's my application controller

class ApplicationController < ActionController::Base
  protect_from_forgery
  before_filter :set_locale

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

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

And my route.rb file is:

scope "(:locale)", locale: /ru|en/ do
  get 'about' => 'home#about', :as => 'about'
  get 'services' => 'home#services', :as => 'services'
  get 'contacts' => 'home#contacts', :as => 'contacts'
end

root :to => 'home#index'
get '/:locale' => 'home#index'

Here's the switcher itself in shared/_header.html.erb partial (I'm using rails_bootstrap_navbar gem)

<li class="dropdown visible-desktop">
  <a href="#" class="dropdown-toggle" data-toggle="dropdown"><%= image_tag(:en == locale ? 'us-flag.png' : 'ru-flag.png') %> <b class="caret"></b></a>
  <ul class="dropdown-menu">
    <li class="nav-header"><%= t(:language) %></li>
    <li class="divider"></li>
    <%= menu_item 'English', locale: 'en' %>
    <%= menu_item 'Русский', locale: 'ru' %>
  </ul>
</li>

Any help will be appreciated. Anyway I'm pretty sure that I have some dumb mistake somewhere. ;)