Still, I'm having second thoughts about continuing with Duolingo after a recent change highlighted an enormous flaw. Since nothing is saved locally, you can dive into Duolingo's courses from several devices. Duolingo uses research on language learning to build its courses, and it uses new research to add to and alter its existing courses. The ability to change courses and better them is fantastic — until you consider what it does to people who are already on those courses. I'm wondering whether it's time to go old school with language learning.