How Duolingo became the most popular language app in the world

Luis von Ahn speaks to Andy Martin about how he went from not having a clue about how to teach languages to creating a platform to teach more than 30

Duolingo’s Luis von Ahn (left) and Severin Hacker (Duolingo)

Two decades ago, Yahoo’s chief scientist came to Pittsburgh to give a lecture at Carnegie Mellon University. He mentioned that Yahoo! was bugged by 10 technical problems it had never managed to resolve. One of them was the fact that scammers were regularly programming their computers to hoover up a million or so free Yahoo! email addresses, to be exploited for no doubt nefarious purposes. And so far Yahoo! could do nothing to stop them. If anyone could solve that problem for them, they would be extremely grateful.

It so happened that Luis von Ahn was in the audience that day. Having taken his first degree in mathematics at Duke, he was then a graduate student in computer science. While working on his PhD he came up with the answer to Yahoo!’s problem – those slightly wonky, distorted numbers and letters that you have to identify to prove you’re not a bot. The tech giants were so grateful they paid him a gazillion dollars for “Captcha” (Completely Automated Public Turing test to tell Computers and Humans Apart). Which left him in 2009, at the age of 30, with an interesting problem of his own: “I don’t have to work ever again – so what am I supposed to do for the rest of my life?”