Europe and China are about the same size. Some regional Chinese dialects are more mutually unintelligible than Italian and French (e.g. Shanghainese and Cantonese), though they all share the same written language.
Xinjiang is as far from Beijing as Lisbon is from Stockholm. While the area has technically been part of China for around 250 years, it has never been part of a unified Chinese civilization. The local Uyghur language is written in Arabic script and over half the population is Muslim.