For what it's worth, when I used to work in the motor trade further into West Wales, customers would come in test drive cars, go through all the process, then often discuss the pros and cons between them in Welsh.
At this point, I hadn't told them that I could speak Welsh - sometimes I would listen to what they were saying and alter my approach accordingly. Other times, I would start conversing in Welsh and their attitude would change completely. They'd start asking me things like "What do you think we should do?, What colour do you think is best?" as if I was a completely impartial friend.
So the moral is that establishing something in common (the more rare, the better I think) is a fast track to building a good relationship.
Advertising in their native language is a good starting point - but and Ad in Hindi then the rest in English would be akin to holding your hand out to shake it, then pulling it back and blowing a raspberry with your thumb to your nose at the last second.
I hope that makes sense. As it happens, I have also considered doing the same thing in the past, but didn't bother after thinking it through.