While flying from MUC back to ORD two weeks ago, I was monitoring ATC communication offered by UA. As we get into airspace controlled by Montreal Center, I notice pilots from AF start communicating with ATC in French.

I thought English has always been the "standard" language for ATC communication, and that one should not use a different language (in this case, the native language of pilots and ATC) unless it's an emergency. I have never heard CI/BR pilots communicating in Chinese, nor have I heard LH pilots communicating in German with ATC. Am I missing something here? Or does it have something to do with "French Pride"?

By the way, our first ATC (from Montreal Center) upon entering North American airspace was probably a rookie. He obviously was not able to handle all the TATL flights that came in at the same time. Our UA pilots have paged him several times and we kept getting ignored. You could tell our pilots were getting frustated from their voice.