Dzongkha, the official language of Bhutan, belongs to the Sino-Tibetan language family (*).

Until the 1960s, Dzongkha was written using the classical Tibetan script. However, in the 1960s, Bhutan adopted a modified version of the Tibetan script called "Uchen," which was specifically designed for the Dzongkha language. 

What makes Dzongkha unique among Tibetan languages is its simplified phonetic structure, distinguishing it from many other languages in the Tibetan group.

Note:

(*) Sino-Tibetan language: A major language group spoken across East Asia, Southeast Asia, and parts of South Asia. It includes languages such as Chinese, Tibetan, and Burmese.