the best way I think, apply the locale id as part of your URL, looks like "/en/articles/1", that's will make page caching quite easy without any additional codes.

Step 1 - configure your routes setting

map.with_options(:prefix => ':locale') do |i18n|
  i18n.resources :article
end

Step 2 - append a before filter to your ApplicationController

def set_locale
  I18n.locale = params[:locale]
end

Magic done. To get more details or examples, follow "this link":http://railscasts.com/episodes/138-i18n for a screencast on Railscasts.com

Your first question is quite easy. While calling URL generator for a model class, it is actually calling it's to_params method.

  class Article < ActiveRecord::Base
    def to_params
      return "#{id}-#{title.parameterize}"
    end
  end

this will returns a pretty id for url.

And the second one, I haven't find out a perfect way to deal with. Maybe other rails guys could help.

However, I haven't totally understand the second question about the "navigation" ;-p

Usually this comes in two conditions:

for static navigation: the navigation contents are static - do not relate with database, just using Rails I18n and compose the translations under "/config/locale"

for dynamic navigation: contents are dynamic - saved in database and will be loaded while requesting this page, pre-execute a query for loading contents and then render a navigation template

# e.g. Init the navigation in sidebar if necessary
# controller
before_filter :load_navigation
def load_navigation
  @navigation_items = NavigationItem.find_all_by_locale(params[:locale])
end

# sidebar template

  
    
    
    
  

Now I got it.

For example, in this url "193-this-is-an-example", only "193" is significative and "this-is-an-example" is useless for Rails application (however it is still useful as a part of friendly url). One target (such as a post, a book, etc) in different language will be saved as different records in database, with different id

# Example controller, maybe ArticlesController
def show
  if params[:id] =~ /^(\d+)\-.+$/
    @article = Article.find($1)
  else
    redirect_to articles_path
  end
end

There is no need to fix the rest part of URL because they are useless while finding an record, just ignore them and your user will not pay attention on the difference between "192-say-hello" and "193-你好". The most important thing is, it works well as we expected, both these two url point to the one article with greeting words in different language. I think that should be what you actually need.