assuming they have a written language. i believe there are a couple of the ethnic
minorities here in china (there are ~55 plus the han) have no written language.
here's a sign at a government office in yunnan province. first column is simplified
chinese, second column some crazy ethnic symbolism, third column is a modified
pinyin approximation of the ethnic language, not the same pronunciation as the
standard chinese.
also some of the groups use the chinese characters, but with an entirely
different pronunciation. chinese television normally has subtitles for all
the chinese who don't, um, speak chinese.
and assuming they can speak the national language. plenty of locations in southern
china where i'd try to speak with the locals........but the only chinese they know is....
...."i can't speak chinese."