[osdiab]

While the Chinese government has forced the majority of young people to learn Mandarin in schools, even just taking a 1 hour train ride from Shanghai to Hangzhou, both cities have local languages that are mutually unintelligible. Elderly people, especially in the countryside but also in the cities occasionally, often don't know how to speak Mandarin at all. But if you mostly hang out with urban youth you should be fine entirely with Mandarin.