Euro ATC,
People will still talk to each other in french in the lunch room, hallways and even between each other at the sector. Believe me, it's not fun when you can't understand what's going on around you.. ie' the swiss germans in the ACC. that talk amongst them.
Welcome to a multinational organisation, you should see our lunchroom conversations...German,Dutch,Spanish,English,Swedish,Bulgari an,Hungarian,French ...just to name a few. The over riding factor that everyone can communicate in English. Don't think that communication is limited to the lunchroom either, it will still happen in the ops room as well, it's just human nature to speak in your mother tongue, but if you need to get your point across you still can, using English.