The film is available on Netflix in several regions. You can check the "Audio & Subtitles" menu while playing to see if the Tamil track is active for your account.
Searching for a Tamil audio track The Dark Knight (2008) is a common request for fans who want to experience Christopher Nolan’s masterpiece in their native language. While the film was officially dubbed and released in Tamil for television and home media, finding a standalone audio file involves navigating a few different legal and technical avenues. Official Sources for Tamil Audio The Dark Knight Tamil Audio Track Download