In the Pali Canon (Cullavagga, V.33.1), there is an account of two monks, Yamelu and Tekula, who asked the Buddha's permission to translate his teachings into Sanskrit, but the Buddha refused and taught:
"Bhikkhus, the Buddha's words should not be translated into Sanskrit. Whoever does so commits a Dukkata offense. I allow you to learn the Buddha's teachings in your own dialect."