I learned Spanish.

I'm from Central Europe, so my mother's tongue isn't English, but learning English was kind of natural for me - all the games, TV shows, movies and the majority of pop music is already in English.

Approximately 3 years ago I signed up for Duolingo and spent +- 20 minutes every single day learning Spanish. Then met Mexican GF and later decided to move to Mexico for some time, which only improved my level of Spanish.

Anyway, it's amazing to see how only 20 minutes per day can compound into speaking a foreign language.

And the fact that you can do it completely for free w/o needing to visit some institution makes it even better IMO.