Buddhism is historically spread from South Asia throughout Southeastern and Eastern Asia.
Because Buddhism reached a wide range of cultural settings, it is particularly diverse. Its broad divisions are:
(1) Theravada Buddhism and
(2) Mahayana Buddhism.
Additionally, a subset of Mahayana Buddhism, known as Vajrayana Buddhism, is often treated as another major division of Buddhism.
Pali, the language associated with Buddhist scripture, was simply one of those common languages. It was spoken in the part of northern India where ancient Buddhists put Buddhist teachings down in writing, after those teachings had been passed down orally for some centuries.