The local language in Cannes is French. The majority of people do know English well, if not they do know the basics so most of the time locals will be able to hold a conversation with you/give directions. Sign posts are in English too.
a real affirmation my longtime best friend who I don't get to see as often these days described me as least weekend. wasn't quite as, "own it girl", as this pin, but it was an authentic, ah-ha moment (Best Friend Day)