Duolingo CEO says language app rooted in bigger mission

Von Ahn initially created 'Duolingo' to give people a free way to learn English.

Luis von Ahn used to be best known as an inventor of the security tool reCAPTCHA, which helps digitise books every time you type those distorted letters to prove to websites you're human.

Now the 40-year-old entrepreneur is better known as co-founder and CEO of a popular language-learning app, Duolingo. The mostly ad-funded app works like a video game, motivating users to keep translating words correctly by rewarding them.