Source: C-16 Population by Mother Tongue

Took me a while the make this map/info-graphic, mostly because of how the data was sorted. I'm sure there are a several mistakes from my side, but also apart from that, in many districts, especially in the Hindi belt, I'm fairly certain that a considerable amount of people returned at least two languages as their mother-tongue/first language, because the numbers simply didn't add up with the population.

Also what constitutes as a language or a dialect is rather subjective and I obviously took some personal liberties such as distinguishing Bhojpuri, Haryanvi, and Rajasthani (Mewari and Marwari as well) as separate languages.