I'm in a four person team that is comprised by me, my sister and 2 other guys.
One of the two other team members seems to be pissed off about something and I am not sure if I need to address it or let it play out.
I noticed when he would usually say good morning with a happy face, the last 3 days it has devolved to "morning", mumble and today no reply at all.
I assumed that he's going through personal stuff but he actually goes out of his way to greet people he sees coming up the stairs or just walk by our office. So that's not that.
After settling in at my desk, I asked him "you OK?" and he replied that he's well and apologized (since he probably was so focused on what he was doing he didn't notice us coming into the room - which I doubt since he notices people at the other end of the building coming up the stairs).
Work-wise we have no conflicts, we work on different projects and we barely need to cooperate and when we do, our interactions don't hint at any problems (there are none or he's a total professional - leaning towards the latter).
Just to mention that both my sister and I are nationals in this country but grew up elsewhere so we don't speak the language that well. We speak the language we learned growing up between us which I think plays a major role in his dislike (or it's just in my head).
My question is, should I approach him and ask him directly if he has a problem or if I have done anything to offend him?
If yes, how should I approach him? Be direct, joke about it or in some other way?