Thavưng, or Aheu, is a language spoken by the Phon Sung people in Laos

Laos

Laos Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ Sathalanalat Paxathipatai Paxaxon Lao, officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west...

 and Thailand

Thailand

Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...

. There are thought to be some 1,770 speakers in Laos, largely concentrated in Khamkeut District

Khamkeut District

Khamkeut is a district of Bolikhamsai province in central Laos ....

. A further 750 speakers live in Thailand.

Thavung makes a four-way distinction between clear and breathy phonation combined with glottalized final consonants. This is very similar to the situation in the Pearic languages

Pearic languages

The Pearic languages are a group of endangered languages of the Eastern Mon–Khmer branch of the Austroasiatic language family, spoken by Pear people living in western Cambodia and southeastern Thailand....

in which, however, the glottalization is in the vowel.http://sealang.net/mk/vietic.htm