Siddhārtha Gautama, the most well known buddha, lived around the fifth century BCE. It is believed that he spoke an Indo-Aryan dialect, such as Pali (pli). Pali is also the language of many early Buddhist scriptures and the Ethnologue says there are nine second-language speakers of Pali.
In the mid-nineteenth century, opera great Richard Wagner discovered Buddhism and began work on “Die Sieger,” which incorporated Buddhist legends.
While the character Wagner and other Europeans will perform in German, the Buddhist characters will sing in Pali, the words having been translated from English.
Read more in “Wagner opera to be revived in a dead language.”