I've heard before that pilots are allowed to speak their native language with ATC in their own countries, but I'm still confused about the risk to foreign pilots in the same airspace, who will then potentially not understand some of the other conversations going on. I realize ATC would still give commands, answers, and clearances to foreign pilots in English, but wouldn't it occasionally be important for the foreign pilots to be able to understand the context of conversations that aren't directed to them?
Is the benefit of that just rare enough that it's not considered worth it?