Which language(s) to translate in for Indian market?

The big question we face all the time from customers - India has 23 official languages, can you recommend to us what languages we should look to translate for our products/services? We take a quick look at the Indian demographics and provide you with some sensible advice for you to make an informed decision. And yes, there are cases where you need to even look at unofficial languages, such as "Hinglish".