First thing to do is to set the locale that is global to the object

SimplyGlobal.locale = :fr

Watch out! You have to set it to nil at the beginning of each request. I suggest you to use a before_filter in your ApplicationController

To translate a string, just use the t method of the string object.

"welcome".t # will become "bienvenue"

You can also use replacement characters

"welcome %s".t("Johnny") # will become "Bienvenue Johnny"

You can specify the language too

"welcome".t(:fr) # returns "Bienvenue"

or use :all if you want an hash of all languages

"welcome".t(:all) # will return {:fr => "bienvenue", :es => "bienvenidos"}