The Bulungan language, also known as Bolongan and Bulongan (both are archaic), is an Austronesian language spoken in Bulungan Regency, North Kalimantan. The language was the court language of the Bulungan Sultanate. The classification of this language is not clear. Glottolog places it in the Sabahan group.
The Bulungan language is predominantly spoken in eight villages in Bulungan Regency, namely:
Consonants , , and are restricted to loan words, and the first two could be respectively substituted with and . The last of three, however, has been dropped during the course of its history ( ('liver') vs. Indonesian ). The phoneme does not exist in the final position, and instead replaced by a glottal stop (), as in ('happy').
There are three diphthongs in Bulungan, all of them only occur word-finally, namely , , and .
Words are stressed on the penultimate syllable, regardless of its structure: mendus 'to bath', mendusna 'go bath now!'.