init.rb

# Include hook code here

class ActionController::Routing::RouteSet::Mapper
  def languages(*options)
    $LANGUAGES = options.map &:to_s # ugly. Any other idea?
  end
end


# Brutal hack, in the guts. May not work with any other version.
class ActionController::Routing::RouteSet
  alias :old_write_recognize_optimized :write_recognize_optimized 

  def write_recognize_optimized
    tree = segment_tree(routes)
    body = generate_code(tree)
    instance_eval %{
      def recognize_optimized(path, env)
        segments = to_plain_segments(path)
        if $LANGUAGES.include? segments.first
          language = segments.shift
          path.sub!(Regexp.new('^/' + language), '')
        end
        index = #{body}
        return nil unless index
        while index < routes.size
          result = routes[index].recognize(path, env) and return result.merge({:lang => language})
          index += 1
        end
        nil
      end
    }, __FILE__, __LINE__
  end
end

class ActionController::Base

  alias :old_url_for :url_for
  def url_for(options = nil)
    q = old_url_for options
    if params[:lang]
      q.sub! /\w(\/)|^(\/)/, '\0' + params[:lang] + '/' 
    end
    q
  end


  def self.requires_language
    class_eval do 

      helper_method :lang
      def lang
        params[:lang] && params[:lang].to_sym
      end

      before_filter :detect_language

      def detect_language
        redirect_to root_url + preferred_language if lang.blank? 
      end

    end
  end

  protected 
  def preferred_language
    $LANGUAGES.find {|l| request.env["HTTP_ACCEPT_LANGUAGE"].include?(l)} or $LANGUAGES.first
  end

end

# Sorry for this. not sure how will affect the perf.
module ActionController::Routing::Optimisation
  def generate_optimisation_block(route, kind)
    ""
  end
end


module LanguageHelper

  
  # Works for two languags, change the title with gettext.
  def language_switch_link(label)
    the_other = $LANGUAGES.find {|l| l != lang.to_s} 
    link_to label, root_url.sub(lang.to_s, the_other.to_s)
  end

  def M_(instance, field = 'name')

    #not in language context
    return instance.send(field) unless self.respond_to?(:lang)

    if instance.respond_to? "#{lang}_#{field}"
      instance.send("#{lang}_#{field}")
    elsif instance.respond_to? field
      instance.send field
    else
      raise "#{instance.class} can't be properly language converted"
    end
  end

end

ActionView::Base.class_eval { include LanguageHelper }