This region is a language boundary rather than a language area, and it contains two large languages that officially do not exist. Angika, spoken across Bhagalpur, Banka, Munger and into Jharkhand, is usually returned as Hindi or Maithili in the census; Surjapuri, spoken across Kishanganj, Katihar, Purnia and Araria, sits between Bengali, Maithili and Assamese and is returned as Hindi. Bengali is a first language in the eastern districts, Urdu is dominant in Seemanchal's towns, and Santali begins as soon as the ground rises to the south.
AngikaIndo-Aryan, Eastern (Bihari group)
The language of Anga, closely related to Maithili and Magahi, with a long-running campaign for recognition and a written literature that has never had institutional support.
Speakers: Around 7.5 lakh returned in the 2011 Census, against field estimates several times higher
SurjapuriIndo-Aryan, Eastern
Spoken across Seemanchal and into north Bengal and Nepal — a transitional language whose speakers are routinely counted as Hindi or Bengali depending on which side of a district line they live.
BengaliIndo-Aryan, Eastern
A first language across Katihar, Kishanganj and the Bengal fringe, with Bengali-medium schooling and a full literary and festival culture.
Seemanchal UrduIndo-Aryan, Hindustani
The urban and madrasa register of a belt where Muslims are a very large share of the population — Kishanganj district is majority Muslim, the only such district in Bihar.
SantaliAustroasiatic, Munda
Spoken on the southern fringe where the plain meets the Rajmahal hills, written in Ol Chiki, and in the Eighth Schedule since 2003 — the one language of this meeting point with full recognition.