This might not be much help... but what about trying to learn their native language? I know for me this would be a real challenge -- I"m horrible at languages, and probably undiagnosed dyslexic. But maybe, showing the interest in being apart of their social activities would be a start? Maybe wait until after the friend leaves and express interest in learning the language and having him help you so that next time the visit goes a little smoother.

I know it's hard right now, but things will go back to normal for you two. Think of it like being in a long distance relationship for a little while. Perhaps request that he still get dinner with you once a week, and maybe a long phone conversation every couple nights just to reconnect? I personally don't really have any tolerance for smoking of any kind (My dad has severe asthma so I find a lot of smells bother me, not to mention if I dated a smoker I'd never see my father again because he can't be any where near it without having an asthma attack), so I would probably bring this up now. But, for your relationship, I'd almost suggest waiting to see how he is once his friend leaves. Perhaps it's just a social thing, and he'll return to his previous habits when his friend leaves.

I'm sorry things are so tough. I am a little curious. You say this is an annual trip and that you have been with your boyfriend for two years? Has the trip happened once before then? How did you handle it then?

Good luck, take care!