I wonder if maybe having one official language that everyone has to learn (i.e. 普通话) allows for greater diversity in local languages. In Europe for examples, there are maybe 20 or so different languages that each have official status in a region that’s more or less the size of a Chinese province, so everyone in that region learns a fairly uniform version of that language and can communicate with other people from that region (Swedes from southern Sweden have no problem understanding Swedes from northern Sweden, even though the geographic distance between them is pretty big). In China, the regional language generally isn’t taught in schools or spoken on TV, but it’s still firmly enough rooted to be people’s first language, so then there’s more splintering, and each town speaks their own version — to the point where two cities in Hubei province apparently can’t understand each others’ dialects. Maybe if there had instead been something like a nine-language policy, the versions of those nine language that people speak would have been much more uniform?