Sign Language?

I haven't actually seen this movie, though it looks promising and if I see it anywhere I'll be sure to check it out, but from the few clips of it that I've tracked out I was a bit surprised that the main characters appear to be communicating in American Sign Language, though from what I understand the movie is set in India. Was this done as a way of paying homage to Helen Keller or is ASL actually used in India? Is it explained in the movie?