I thought some folks might be interested in an article recently published in IEEE Spectrum:
How Duolingo’s AI Learns What You Need to Learn: The AI that powers the language-learning app today could disrupt education tomorrow.
Info on the authors is somewhat buried, so I'm copying it here:
Klinton Bicknell is head of AI at Duolingo. Before joining Duolingo in 2018, he was a professor in the department of linguistics at Northwestern University.
Claire Brust is an AI-research engineer at Duolingo.
Burr Settles was formerly the director of research and head of AI at Duolingo.