En (autonym: aiò<sup>53</sup> or eò<sup>33ÃÂ</sup>, also known as Nùng Vẻn) is a Kra language spoken in Vietnam. Before its discovery in 1998, En language was undistinguished from Nùng, which is a Central Tai language closely related to Zhuang. In the late 1990s, Vietnamese linguist Hoàng VÃÂn Ma had first recognized that it was not a Tai language, ultimately leading to field work distinguishing En as a separate language. Researchers have determined En to be one of the Buyang languages.
The speakers of En live in northern Vietnam near the border with Jingxi County, Guangxi. In 1998, En speakers were found 12 km to the east of HàQuảng city in Ná»Âi Thôn village, HàQuảng District, Cao Bằng Province.
En has 6 tones: (/54, 243, 332, 33, 212, 32/).