You have to set the locale in SimplyGlobal.locale at every request. I suggest you creating a before_filter in your ApplicationController that sets the locale.

application.rb

class ApplicationController < ActionController::Base
	before_filter :set_locale

	private
		
	# Set the locale
	def set_locale	
		SimplyGlobal.locale = params[:locale]
	end
end

Then, create a connection that uses a locale. In the above example, we could write URLs like fr/home/index.

routes.rb

map.connect "/:locale/:controller/:action/:id"
	:requirements => {
		:locale => /fr/es/
	}