Original sentence: The area was probably Indo Aryan in culture and part of the Vedic civilization of ancient India, but at the time of the Buddha's birth, Kapilavastu was a minor state on the boundary of the Vedic civilization; it is even slightly possible that his mother tongue was not an Indo-Aryan language, although he most likely spoke a Prakrit decended from Sanskrit
Edited sentence: At the time of the Buddha's birth, the area was at or beyond the boundary of Vedic civilization, the dominant culture of northern India at the time; it is even possible that his mother tongue was not an Indo-Aryan language