Phu Thai is a city located in Vietnam. While the provided source material does not offer specific geographical details regarding its location within the country, it identifies the name as associated with a Southwestern Tai language.
The Phu Thai language is spoken across Laos, Thailand, and Vietnam. Although it maintains distinct characteristics from Isan and Lao languages, it has been influenced by them in regions where those languages are predominant. Systematic comparisons between Phu Thai and other Tai languages, such as Tay Khang, have not yet been conducted extensively enough to produce definitive results.