Over time you will figure out who is who here.
Though I think it's a good idea, I don't mind being able to see person't native language displayed under their location on the left of the post's frame, similar to that done on WordReference. On the other hand, this feature is of little practical use because if you, for e.g. spot Sweden under Hanna's location this is not going to help you in any other way than to compliment her on her good command of English.
In addition, we have a couple of threads like "what's your native language"; you can look them up.
The only bad thing about such threads is that it's practically impossible to get a random person's mother tongue found in them.

Kindest regards,
Native Russian Medved