I see the reasons why local languages are allowed to be used. After all, Geneva is in a country one of whose official languages is French.
But I guess it also means that if those British pilots I heard on the same frequency don't understand French (not to presume of course - they may speak fluent French like most of us
), then they also didn't understand what was said between the ATCO and French aircraft. That can't be great.
Maybe it doesn't matter. I'm certainly not in a position to judge. Nor am I trying to re-write the rules. I am, simply, a bit surprised.