Learning languages in Duolingo is completely free – now and forever – with no ads or hidden fees. Wondering how that can be? It’s because you create value by translating real-world documents while you’re learning.
Here’s how it works: Somebody who needs a webpage translated uploads it to Duolingo. That document then gets presented to Duolingo students who can translate it in order to practice the language they are learning. When the document is fully translated, Duolingo returns it to the original content owner who, depending on the type of document they uploaded, pays for the translation.