Speak whatever language you want.
If I am a guest in your country I don't care what language you speak on the radio. If I happen to speak yours I will try to use it as well.
I used to give a crap about this issue until I realized the TCAS works pretty da.n well anyway.
Just for the record I do speak 4 languages fairly well, after six beers I can do a couple more languages in a pinch. I am sick of learning though, so I will not learn any more.
Spasiba.