Buddypress multilingual

Here I have a question,I would like to have a buddypress multilingual,I would like the user to only have the activity stream in the language they choose but in the same time if the want to see what happening in the other language they have access to it.

My first thought was 2 different domain name,that I could Link together and find a way to import the users from one side to the other.But it seems to me not so convenient.

Second one,I thought of a plugin that switch languages,but I still have the issue of 2 language in the activity stream.Plus when I try I had many issue with some part of the theme not changing language event with the po file.

third option,I’m not sure about that one,but might be the one,if a sub-domain share the same db than the domain,than I could install WordPress in different language on each one of them.But I’m not sure that 2 WordPress on one database is safe.

Anyway if someone had the same problem than me ,tell me what was your solution it would be appreciated