In OTL, China has been divided as often as not, but after a while the centralization of the empire would be restored. There was the Springs and Autumns and then the Warring Kingdoms period, the Three Kingdoms, the Dynasties of the North and South, etc... And, technically, contemporary China is divided between the People's Republic on the mainland, and the island of Taiwan. If what you're aiming at is permanent, rather than temporary, cultural and political division, then I think gaijin has the best suggestion: no First Emperor to unify the writing system. It's likely a lingua franca would develop anyway among the scholarly and clerical classes, but it would be more like Latin in medieval Europe, and wouldn't prevent the gradual emergence of local vernaculars with their idiosyncratic calligraphies. Interestingly, this might make Chinese civilization significantly more expansionist than it was in OTL, with the political and military emulation between rival kingdoms leading to exploration, conquest, and the more thorough application of all the technological breakthroughs that Chinese engineering came up with, but which in OTL were not used to their full potential. Let it be reminded that, by the 11th century, the Chinese had the printing press, the compass, and the multiple rocket launcher. In OTL they were content merely preserving stability and keeping the barbarians at bay. In a "divided China" TL, they would be much more like the early modern Europeans, with considerable consequences for the rest of the world.