I wasn't talking about Mandarin and Cantonese as "dialects", I was talking about different dialects of Mandarin as spoken in Beijing (which the official dialect is based on) versus e.g. Sichuan. Those are mutually intelligible similar to the varieties of English, but they are markedly different in details of their pronunciation, word choice, and occasionally grammar. European languages aren't the only ones with hard-to-understand regional dialects.