There is one form of Chinese that is considered the standard, and that is Mandarin. Mandarin is the official language of China and Taiwan. But there are 13 different dialects that are spoken in various regions, and are mutually unintelligible. That means that if you speak only one dialect, you won't understand anything said in another dialect. Other dialects include Cantonese, Xiang, Wu, Hakka, and several others. Most Chinese people learn at least one other dialect, and it isn't uncommon for someone to be common in both Mandarin and Cantonese, the two most popular ones.