The Tamil kings of India had great influence on SE Asia during the Chola period.(1,2) Sanskrit was certainly used in SE Asia(3). Mostly ceremonial like Latin and used only by the ruling class I think

1.https://en.m.wikipedia.org/wiki/Chola_invasion_of_Srivijaya

2. https://en.m.wikipedia.org/wiki/Chola_dynasty

3. https://en.m.wikipedia.org/wiki/Shailendra_dynasty -