Thread:Project:Support desk/ switch: Lang doesn't work for log-out visitor

Good day, I use to have the same page displays in the language chosen by the visitor. With &setlang=fr or en in the url, it works for log-in user. However, for visitor not logged in, even if they add &setlang=fr in the url, the page remains in English and only the title is in French. It had been tested on Google Chrome. And the tested page is http://wikimedia.ca/w/index.php?title=Projects/National_Contribution_Month&setlang=en or http://wikimedia.ca/w/index.php?title=Projets/Mois_national_de_la_contribution&setlang=fr. How come? Thanks,