East Asian Languages

East Asian languages belong to several language families that are generally believed to be genetically unrelated, but share many features due to interaction. In the Mainland Southeast Asia linguistic area, Chinese varieties and languages of southeast Asia share many areal features, tending to be analytic languages with similar syllable and tone structure. In the first millennium AD, Chinese culture came to dominate east Asia. Literary Chinese was adopted by scholars in Vietnam, Korea and Japan, and there was a massive influx of Chinese vocabulary into these and other neighboring languages. The Chinese script was also adapted to write Vietnamese, Korean and Japanese, though in the first two the use of Chinese characters is now restricted to university learning, linguistic or historical study and artistic or decorative works.

The languages of Southeast Asia and East Asia belong to several language families.

The Austroasiatic languages include Vietnamese and Khmer, as well as many other languages spoken in areas scattered as far afield as Malaya and eastern India, often in isolated pockets surrounded by the ranges of other language groups. Most linguists believe that Austroasiatic languages once ranged continuously across southeast Asia and that their scattered distribution today is the result of the subsequent arrival of other language groups.

One of these groups were the Tai–Kadai languages such as Thai, Lao and Shan. These languages were originally spoken in southern China, where the greatest diversity within the family is still found, and possibly as far north as the Yangtze valley. As Chinese civilization expanded southward from the North China Plain, many Tai–Kadai speakers became Sinicized, but some migrated to southeast Asia. With the exception of Zhuang, most of the Tai–Kadai languages still remaining in China are spoken in isolated upland areas.

...
Wikipedia