I find reducing distraction is best served by providing sufficient means for a person to isolate oneself physically. If you feel like the conversation is a private one between yourself and another, the correct approach is not to speak in a different language. Not only does that not scale, it only solves your problem, you don't get to decide how the junior feels about it, and neither do they.

If you're a senior, you should have been a junior at some point, so I'd put the question back to you. Do you feel like sitting next to two people speaking in a completely different language would eliminate distraction? For me, I'd still be getting the noise of you speaking, but then I'd also be wondering why two members of my team have openly excluded me from a conversation happening in my presence. It doesn't encourage me to try and do better, and it makes your duties opaque. The way you describe it also sounds rather imbued with infantilism; "don't worry what we're chatting about, just type your little code while we do important grown up stuff".

Would you have been open to her asking you to stop if she felt that was ruining her productivity? It really just seems like a barrier that isn't necessary and shouldn't be there, waving it away as though they should have different feelings about it.