Pali is the language of the Hinayana or Theravada Buddhism, a derivative of Sanskrit. It was the ancient language of the Vedic Aryan peoples, native to the indian subcontinent and in its vulgar form it was the common language of Magadha.
The Pali language is in some sacred texts religious texts of Hinduism and all Therava Buddhism texts.
The older Buddhist canon was written in Pali, but it is now employed primarily for the Hinayana; the Mahayana, «Greater Vehicle,» rewrote portions of the cannon in Sanskrit. In Pali, the Sanskrit terms such as dharma and nirvana became dhamma and nibbana. Pali was the language used by Indian Buddhists in their cultural, trade, and religious penetration into Southeast Asia, or Indochina.
Today Pali doesn’t exist as a language but it is used to read an study ancient scriptures. There is a society to promote the study of Pali in Europe, the Pali text society.
To know more about Pali Alphabet, phonology, morphology https://en.wikipedia.org/wiki/Pali
Rice, Edward, Eastern Definitions: A Short Encyclopedia of Religions of the Orient, Garden City, New York, Doubleday, 1978, p. 281