How Duolingo became the most popular language app in the world

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?”

And the answer to that problem was Duolingo, the most popular language-learning platform in the world. Von Ahn had meanwhile become a professor at Carnegie Mellon. His reasoning was as follows: I want to do something to help people, especially in poorer countries, notably Guatemala (where he was born). Most people get a bad education. I’m an educator. What is the best single thing I can offer that will help them get on in life? Something that will give equal access to everybody?

Learning English can change your life. If you can speak English it opens doors to better careers and increased earning power. So, in 2012, von Ahn (together with his fabulously named research student, Severin Hacker) conjured up a free English-learning app. But then people who already spoke English were clamouring to learn other languages. Now Duolingo hosts some 30-odd languages (including Navajo and Klingon) and is developing more all the time.

“I owe it all to my mother,” Luis von Ahn says modestly. “She was a doctor. We were not rich. But she spent all her money on giving me a rich kid’s education.” She also bought him a Commodore 64 computer when he was eight years old. “I actually asked for a Nintendo, so I was quite upset at the time.” He had to work out how to use it properly in order to be able to play Space Invaders.

Von Ahn’s mother is of Spanish descent, his father German, and his name already contains two languages, so he was born to be a linguist. His English is perfect, he has become “quite good” at Portuguese, and is currently learning French and Japanese.

It took the American army to work out what makes the difference between being good or bad at languages. In the wake of recent conflicts, they wanted to train up a whole bunch of Arabic speakers in a hurry, but they didn’t want to waste a load of money on soldiers who weren’t going to pick it up. A lot of analysis enabled them to boil linguistic talent down to one big thing: the willingness to sound extremely stupid at the outset. That’s how it is when you’re struggling around picking up the rudiments of another language. So long as you’re relaxed about appearing to be an idiot, you can learn a language at any age, says von Ahn. “It doesn’t matter how old you are. You can be 90. You may not become poet laureate but you can get better.”

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In the beginning Luis von Ahn and his collaborators didn’t have a clue how to teach a language. “We didn’t know, we just read a few books.” But they quickly realised that they had the tools to improve what they were doing. A lot of people starting using the app, so they had masses of data to hand. Was it better to teach plurals before adjectives or adjectives before plurals? They simply ran a test on the next 50,000 users: half of them did it one way, half the other, so they could work out which one was most effective (answer: it depends on which language you’re learning and your own native language).

They also started recruiting people who could actually teach languages too. “We’re not putting teachers out of a job,” von Ahn points out. “Teachers are good at motivating. Duolingo plus a teacher is better than doing Duolingo on your own. But not everyone has access to a good teacher.” 40 per cent of language classes in the US now use Duolingo.

The great thing about Duolingo – as I know having used it myself – is you can still learn for free. If you want to turn off the ads, you can pay to have the premium option. French and Spanish are still the most popular languages in the United States. Elsewhere it’s English. Welsh is big in the UK. But one of the recent growth languages is Korean. “It’s partly to do with K-pop,” says von Ahn, “partly Squid Game and other Korean dramas.” Japanese is more popular (and easier) than Chinese. “Chinese scares a lot of people off.” But they’re working on upping “engagement” and keeping novices on track: “We’re trying to make it more fun.”

Personally, I found the “streak freeze” came in very handy. And the regular weekly reports (could do better, generally) kept me in line.

The fundamental logic behind Duolingo was not languages per se but education. So it’s natural, with Luis von Ahn at the wheel, that they should start introducing mathematics into their curriculum. “The mobile phone enables us to reach more people cheaply. We can reach 4 or 5 billion people without building a school.”

I confessed to Luis that I had always struggled with quantum mechanics. “Don’t worry,” he says. “We’re not going to start with quantum mechanics.”

@andymartinink