Not sure if this helps or not but from the data I can see that there have been 97776 unique players who have played at least 1 ranked match since the 1st May. Of these 23329 of them have played at least one match using Bengalis, Dravidians or Gurjaras.
To me that implies at least 23k copies of the DLC have been sold as a lower limit with a conversion rate of roughly 25% (I would guess this is overestimated due to ranked players being more dedicated to the game than pure casual players).