If there is nobody else in the room at the moment, and you want to explain things, I suppose it is okay. However, if two people began speaking in a different language in front of me (in real life) and they knew I didn't speak it, that would be rude. Considering that SE is a group of English speaking sites, your use "constitutes knowledge" (I am not a lawyer, nor representing SE, just stating my perception of the rules.)
The other thing to consider is the transcript. People who read it will likely not understand it.
Additionally, since SE is an English language website, do not create rooms for other languages. (Although, I have spotted a room in Russian...)
For better of for worse, language barriers tend to frustrate not only those asking questions, but also native English speakers who try to answer the questions. I suggest sticking with English here.