The way that Duolingo, the popular language-learning app, hounds you to keep up your daily lessons has become a meme. But it’s so insistent for a reason. Being addictive is basically the app’s entire business model.

The lessons, which are designed to be as game-like as possible, are meant to take about three minutes each. Users answer questions and solve problems in the languages they’re learning, trying not to strike out too many times and be sent back to the beginning. And if you go 24 hours without opening the app, it sends you a friendly if firm little poke, with a cute owl.

There’s a lot of business behind this model of language learning. Rosetta Stone, which costs $120 for a year’s worth of lessons, has 500,000 customers learning 25 languages. Babbel, at $85 a year, has over a million customers. Duolingo, which is free with ads, announced last year that it had reached 30 million active users worldwide. English is the most common language being learned, with Spanish a distant second. Fewer than 2 percent of those users pay for the ad-free version ($84/year), generating a meager $36 million in 2018, but newer features are projected to generate more revenue.

Luis von Ahn, who created the app seven years ago with his partner Severin Hacker, hopes to take the company public next year as an IPO. He also hopes to add another revenue stream—the Duolingo English Test, a standardized English proficiency exam to shop out to universities. Currently, all American universities use the TOEFL (Test of English as a Foreign Language) exam, which costs students approximately $215 to take. He wants his DET to become a cheaper, remote-access version of the TOEFL with the same credibility.

Critics point at the app’s algorithm-driven language instruction as being ineffective in a human setting, and von Ahn does, to a point, agree with them. So he added a user-driven website where people can arrange events local to them to try out their new skills. And he’ll keep adding features and functions, he says, “until most everybody in the world who is trying to learn a language is using one of our products.”

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