After Hindi, what other Indo-Iranian languages should Duolingo add?
Here are my choices:
For the Indo-Aryan branch: Urdu, Bengali, Punjabi,
For the Iranian branch: Farsi, Kurdish.
What do you think?
To clarify my previous reply: it seems to me that languages like Sanskrit, Old Norse, Latin or some form of ancient Greek could be at least as successful here at Duo as Russian, Ukrainian or German. Probably there are people among us who could write good courses for these languages, and indeed people have applied to develop courses for some of them. But until Duolingo chooses one or more of these languages to incubate, we won't have the chance find out.
Since Duolingo already has English for Bengali speakers and English for Punjabi speakers on the way, adding Bengali for English speakers and Punjabi for English speakers after those courses are finished (and not immediately after, the people making the courses deserve a break!) is an obvious next step. :)