HISTORY OF THE BENGALI LANGUAGE - বাংলা ভাষার ইতিহাস
Bengali belongs to the easternmost branch, called Aryan or Indo-Iranian, of the Indo-European family of languages. Its direct ancestor is a form of Prakrit or Middle Indo-Aryan which descended from Sanskrit or Old Indo-Aryan. Sanskrit was the spoken as well as the literary language of Aryandom until circa 500 B.C., after which it remained for nearly two thousand years the dominant literary languages as well as the lingua franca among the cultured and the erudite throughout the subcontinent.
Like Sanskrit, Apabhramsa-Avahattha was a literary language, and in the available records it shows remarkably little local variation; practically the same form of the language appears in the poems written in Gujrat and in Bengal. But the spoken language conditioned by the regional linguistic and ethnic environments took up the different regional New Indo-Aryan languages. The emergence of these New Indo-Aryan speeches was not all synchronized. But some of them, including Bengali, certainly originated by the middle of the tenth century at the latest.