Vrajawali - The Language of Vraja
The language in which Sankaradeva wrote his songs (Borgits) and plays, as did his successors, was the localized variant of the then lingua franca of Northern India and was termed in Assam as Vrajāwali.
Vrajāwali or Assamese Brajabuli as it was formerly known, is the vehicle of an old and impressive literature, virtually invented single-handedly by Sankaradeva. Scholars do not seem to agree about precisely what sort of language Vrajāwali is. It is a dialect which seems to have Maithili as its basis, to which is added Assamese with a sprinkling of Western Hindi.
In fact the very style of these works both in prose and poetry which is replete with tatsam words set in highly ornate design, points to a well developed and considerably standardized literary vehicle, which was commonly used in the whole area between Gujrāt in the West and Assam in the East and served the cultural and literary need of this extensive region. Its connection with the Vraja Bhumi or Vrindāvan-Mathurā region made it more popular among the Vaisnava preachers who took up the cause of vernaculars for the first time.