French, Italian, Spanish... shame on you!
Yeah, yeah... We know, we know...
Nicholas49,
being a French controller, I'm (ashamed to be) used to use English and French on the same Frequencies.
On pilot's request.
The pilot is always the first to speak. For safety reasons, I won't play the game of speaking English with a pilot who speaks French. I don't know if he's able to speak English. Just for the same reason, I speak English with a pilot who speaks English. He might not understand if I speak French.
As Singapourcanac said, the translation (or explaination of the situation) is given to the pilot who is not supposed to have understood, when I suspect he could be interested. Either French or English.