In which language or languages were most of the sutras compiled?
Shakyamuni Buddha spoke in a language known as Magadhi Prakrit. According to this article https://www.quora.com/What-language-did-Gautama-Buddha-speak-according-to-Indian-mythology-and-why-is-it-significant there are no written records in his language. Instead, they were later written down in Pali, Sinhalese, and Sanskrit.