Hello. I just downloaded this app.

I thought of the same thing once, whether it is polite to talk to each other in a different language than the one that's spoken by others who might be listening.

And I think that there are many ways to look at it.

As of those who speaks a language that's different than the one being spoken, they do possess the knowledge of this language whereas the others don't. An analogy would be when two people who studies psychology use terms to talk to each other, temporarily leaving their friend out of the conversation. Is this necessarily inappropriate? I think naturally, people who don't like the idea of not knowing things (or are not in the mood of hearing other languages) would show rejection toward such action, and people who are afraid of not knowing things would be ashamed of not knowing. These feelings could annoy them or motivate them. To each his own. To me, it's at least understandable. But how I feel does not depend on what language others use more than it does myself.

Think of it as, two foreigners who travel to a country that speaks a different language, they speak to each other in their own language there. The natives could be annoyed for they do not understand what they are talking about. But I don't think they would go through the trouble of recording it and having it proved whether they are badmouthing them or not, just for the sake of it.

I'm not qualified to say that this is probably just another case of cultural difference. But I do however feel that English speakers may have a hard time understanding this given that the current state is that the majority of the world seems to be studying English due to globalization.