In Quebec or Ottawa area, ATC is bilingual. They will reply in whatever Language you started your com with.
To keep track of who's speaking what, for the French one they will highlight their flight progress strip in yellow.
While I'm pro English on RT, I had few instances where reverting to local language (French) in unusual situations greatly raised safety while shortening the amount of talking and misunderstanding.
This was in Algeria and Mali for instance.
You cannot expect to hear perfect English in every corner of the globe.
Same, you cannot expect to speak every language of everyplace you will end up flying.
And Plastic787 while your example of situation awareness is admirable and certaily saved the day (united 1448) a common language didn't for this one.
US Air flight 1493 ground collision with a metroliner in LA