Indochina: northern Thailand east to Vietnam, west to eastern Myanmar, and southern China south of the Salween
The Indochinese grey langur is a species of Old World monkey native to East and Southeast Asia. It is found throughout Indochina, from northern Thailand east to Vietnam and west to eastern Myanmar, and north to southern China south of the Salween River (Wikipedia, general species account).
Unlike langurs that live in karst forests and are largely terrestrial, it inhabits old-growth evergreen forests and has a largely arboreal lifestyle.
Description: Wildlife of Vietnam guide, Wildlife of Everywhere (wildlifeofeverywhere.com); general species information paraphrased from Wikipedia (CC BY-SA)
Mammals of the World