If you want to or are learning a new language, use the app Duolingo.
This app was created by Louis Von Ahn, a brilliant professor and businessman at Carnegie Mellon University. He is probably best known as the inventor of reCaptcha and how he began using the time people spend verifying their identity for purchases to digitize books and street signs.
Duolingo was built on the premise of giving access to language and motivating people to return. It’s UX reflects that by creating milestones, maintaining a streak, and gamifying the process in whole. This app is designed to be used intermittently during down time as a social media replacement, and can easily be incorporated into your routine if you have the desire to do it.
I am a huge advocate for Duolingo because I was able to advance past Italian 1 in college after using it for only 2 months, and went on to set the curve in Italian 2 because I was over prepared by the app. I can attest to the habit forming capabilities of it and was truly motivated to learn the language.
So apple, android, or whatever you may have, Duolingo is in the app store and available now, and is currently offering 30 different languages. Give it a try and watch your downtime become seamlessly more productive studying a foreign language.