No, the Chinese written language is not common to all sino languages; most local languages are not written down, ever. People write in Mandarin. A century ago,

No, the Chinese written language is not common to all sino languages; most local languages are not written down, ever. People write in Mandarin. A century ago, people wrote in classical Chinese, which is an entirely separate literary language. When you go to Shanghai or Chenzhou you see signs, books, advertisements, etc. written in Mandarin, not the local languages of Shanghainese or Dzao Min. There are some exceptions -- Cantonese and Yi come to mind -- but these are very specific historical exceptions. I purposely chose Swedish from the Germanic language family to prove a point. When this topic ever does get brought up, people usually make the comparison to Latin and the romance languages in Europe, harkening back to a time when all written communication was in Latin, and the vulgar or Germanic languages were spoken only. But would you seriously claim that Latin was the written form of Old German? Or that the Latin literary culture of the time was inclusive and representative of Germanic cultural norms? Many (most, depending on how you count) of the local and minority languages in China are only distantly related to Chinese, in the same way that Swedish and Portuguese are both Indo-European languages. What we call China was a culturally, ethnically, religiously, and especially linguistically diverse place when it was politically unified by Qin Shi Huang 2200 years ago. Many of those languages still exist today, in the same regions. But thanks to 2,000 years of linguistic suppression these languages have no written form or literary culture, and very few people are even conscious of the loss.