What little I have studied of Sanskrit was kind of amazing. Seems like I already knew about 1/3 of it, it is familiar somehow, like we still speak it to a degree, even in English, although I don't know if Sanskrit was ever an actual commonly spoken language.
From Wikipedia:
Sanskrit is spoken natively by the population in Mattur village in central Karnataka. Inhabitants of all castes learn Sanskrit starting in childhood and converse in the language. Even the local Muslims speak and converse in Sanskrit. Historically, the village was given by king Krishnadevaraya of the Vijayanagara Empire to Vedic scholars and their families. People in his kingdom spoke Kannada and Tuluva.