Apparently, you would say, "It's all Telugu to me!"
In Arabic, you would say, "It's all Hindi to me!"
Over at Language Log, Mark Liberman presents a directed graph of which language is used to denote incomprehensibility in a given language.
Among the Indian languages, there are two -- Telugu and Hindi -- at the receiving end of this graph, but none at the other end.
I couldn't think of a similar phrase in Tamil, but seriously, how do you say such a thing in any Indian language? If you have an answer, hop over and tell Liberman!