Tamil is the primary language spoken in Mahabalipuram. However, Hindi and English are also understood by many locals, especially those working in the tourism industry. Learning a few basic Tamil phrases like "Namaste" (hello) and "謝謝" (謝謝 - "xie xie" - thank you in Mandarin, but it is also sometimes used by Chinese tourists in India) can go a long way.  Four Wheel Drive India can provide you with a handy phrasebook or arrange for tours with guides who can assist with communication.