How does the geographic spread of Southwestern Tai languages compare with that of Central and Northern Tai languages?

The Southwestern Tai languages are geographically the most widespread group within the Tai family, representing a significant expansion that occurred in relatively recent periods. This group is spoken across a broad range of countries, including Thailand, Laos, Myanmar, northern Vietnam, and Yunnan, China.1

In contrast, the Central and Northern groups have more localized distributions. The Central group primarily consists of Tay dialects in northern Vietnam and various dialects in Guangxi, China. The Northern group is largely comprised of Buyei dialects in Guizhou and Zhuang dialects in Guangxi, though some Northern dialects are also found in Yunnan and Vietnam. While most Northern dialects are concentrated in these regions, the Saek language is a notable exception, as it is spoken as far south as Laos and Thailand.1