Why should everyone speak the same language?
Well because ATC can make mistakes, I have been in paris cleared to line up from an intersection when a French aircraft has been cleared to take off from the full length. Fortunatley I speak french. I'm sure also that we all remember what hapeened one foggy day at paris when the English pilot didn't.
In Germany they manage to speak english for all clearances but sometimes revert to german if the query is more complicated, would it be that difficult for the french to operate on this basis.
Though really why have this debate at all we all know the french will all do exactly as they like with little interest in everyone else.