Quote from this article:
That's why, analysts say, the film has traveled so well outside of Tamil Nadu. An inability to understand Tamil is no barrier to figuring out what's happening on screen.
(A non-Tamil-speaking American reporter, who sat through all three hours and 20 minutes of "Sivaji," can attest to this.)
"Sivaji" is not a Bollywood production, and Rajnikanth is not a Hindi-speaking Bollywood heartthrob. The movie was shot here in the southern state of Tamil Nadu, and the dialogue is in Tamil, a language spoken by more than 70 million people.