DuoLingo business model
I have been wondering why this all can be free. At least part of the answer is in this talk:
I'm learning Swahili and the good news is that this good for the Swahili speaking communities as well, because more texts translated into Swahili will be available. Awesome.
That's out of date. The translation business model has been dropped and Immersion, the part of the website where translations were done, has been taken down.
I think the current business model is still being fleshed out, but so far it involves the use of ads on some platforms and the availability on some platforms of Duolingo Plus, which allows you to work offline and also, I believe, to avoid the ads.