help for changing the language, locale

[Miren Urkijo]

HEllo y havo one struts aplicaicon.
if into the borwser i change the locale, into the browser properties, my 
application load the properties files well.
i am thinking for making onw struts action for changing the language, thelocale 
but i dont knows how to change it.
can anybody says me how must i make it?
thanks