I found a similar request to this for RSS feeds, but not the "unread posts" link at the top of each page. I also searched for "language" but got about 40 pages of hits, not totally surprisingly as people talk about the "C language".
Could it be changed so that "unread posts" only shows user-specified languages? Much as I would like to help answer questions in French, Scandinavian, and Portuguese, I don't speak those languages (or indeed, anything other than English).
After a good night's sleep the number of unread posts seems to be multiple pages long, making it a daunting task to check them all, at the same time glancing down to see if they are written in a language I'll understand.
Presumably the problem also applies, the other way around, for people who don't speak English.
What would be simple enough is a series of checkboxes per forum user. They could all be initially checked (eg. you will read all languages) and then you go in and uncheck the ones you don't understand.