Hindi is by far the most common language of the state, understood by all. There is a significant number of Benagli speaking people also. They are descendants of the settlers from the old British Presidency of Bengal. English is the language of commerce and is spoken by the educated masses. As over much of India, a combination of Hindi and English (sarcastically dubbed "Hinglis") is the language in the homes of middle-class Biharis.
In addition people speak many dialects in different regions. The major dialects are: Bhojpuri, Magahi and Maithili. Bhojpuri is spoken in the districts of Champaran (East and West), Saran, and Shahabad. Magahi is the dialect of Central Bihar, i.e., the districts of Patna, Gaya and Bihar. Maithili, and its variants, is the dialect of the people in the north-east, i.e., the districts of Muzaffarpur, Vaishali, Darbhanga, Samastipur, Saharsa, Purnia and Bhagalpur.
Of all the dialects and languages, only Maithili can be classified as a distinct and uniquely Bihari language. It has a very old literature of its own. (Hindi, as a distinct literary form, came about only very recently - towards the turn of this century.) The famous poet, Vidyapati, of medieval Bihar, was the composer of lyrical poems in Maithili. These songs are devoted to the worship of Lord Krishna and Shiva. Shrimati Vindhyabasini Devi is a current exponent of the songs of Vidyapati. The French music publishers, Ocora, have published a compact disc of her Vidayapati's songs. (Ocora C580063, "Mithila Chants d'amour de Vidyapati", with Jawahar Lal Jha and Ganesh Kant Thakur)