This actually isn’t true anymore. They stopped the contributor program and started doing it in-house, or at least paying the contributors: https://blog.duolingo

This actually isn’t true anymore. They stopped the contributor program and started doing it in-house, or at least paying the contributors: https://blog.duolingo.com/ending-honoring-our-volunteer-contributor-program-2/ https://blog.duolingo.com/ending-honoring-our-volunteer-cont...