I guess only the "speak well enough" is related to dialects.
The other 30% I think he is referring to people that speak cantonese, and all other interesting languages that exists there, including the mongolian languages (almost everything in China west of the great wall, was originally part of mongolia, like Tibet for example... and thus they have not much to do with China actually, specially Han people).
I hope someday people will figure a way to keep mongolians peaceful without erasing their culture or resorting to extreme tyranny.