If you are a mono-lingual American, it can be helpful to know how native speakers of other languages often pronounce English, so you can understand them more easily. China is a huge country, and Mandarin is spoken differently in various parts of China. For some people, Mandarin is actually their second language, not their first. People in India speak somewhere between 780 and 1683 different languages, although reportedly only 21 are officially recognized.
Have you ever had difficulty understanding someone’s pronunciation, even if he or she knows how to speak English? It can be very frustrating for both the speaker and the listener.