While in his teens, growing up in a family running a candy factory in Guatemala, Luis von Ahn said he often fantasized about creating a gym anyone could join for free.

Now 34, von Ahn, an IT entrepreneur and associate professor of computer science at Carnegie Mellon University in Pennsylvania, said he thought a gym could be made free for anyone to use if all the kinetic energy of the people using the exercise equipment was converted to electricity and sold to the power grid.

Unfortunately, von Ahn soon learned that human effort is an inefficient way to generate electricity.

“It’s not a very good business model because a gym membership is about $50,” he said. “To make $50 off of people doing that is very hard. They have to run for a long time.”

But he has stuck with the idea of harnessing the effort of individuals and reusing it for something else.

Von Ahn, also CEO and a founder of the language-learning application Duolingo (www.duolingo.com), was visiting Japan this week to mark the launch last month of its Japanese-language version. He launched the free smartphone app two years ago with Severin Hacker, a student of his at Carnegie Mellon. Named by Apple as the iPhone app of the year in 2013, it now offers services in 16 languages and boasts 30 million users around the world.

Like many language apps, Duolingo offers vocabulary, translation, dictation and speech lessons, with the level of lessons going up as the learners clear questions.

What sets Duolingo apart from other education apps, however, is that it doesn’t rely on advertising or subscription fees for its revenue. Much like the free gym idea, it is designed to provide language education without a charge while channeling the users’ efforts into something else: translating content such as news articles and restaurant menus for real-world businesses.

The app, which doubles as a crowdsourced translation service, will be in great demand over the next few years as the need for a free language-learning tool grows, especially in the developing world, von Ahn said.

Language education “is very big in the world — 1.2 billion people are learning a language in the world,” von Ahn said during an interview in Tokyo. “A majority of them are in the developing countries and they are learning English. And they are also of the low socioeconomic class, and the reason they are learning a language is to get a job. (But) to learn a language costs a lot of money, so we wanted to make something that was totally free.”

One of Duolingo’s clients, for example, is CNN. Duolingo gets paid by CNN to provide its articles in different languages. After hours of studying a new language, users — non-native learners of English — are invited to read the articles in English and translate them into their native language for Duolingo, which then sends them back to CNN.

Von Ahn has a track record in such “killing two birds with one stone” projects. ReCAPTCHA, a program he invented in 2007 and sold to Google, is a common feature on many websites, where the program blocks spam-sending “bots” by having visitors type distorted characters shown in a box to prove they are human. By deciphering the characters, people are not only authenticating themselves, but also digitizing a word from an actual book.

As for Duolingo, von Ahn acknowledges that the project is still in the red and is mostly financed through $38 million raised from venture capital funds. But despite the app being only two years old and von Ahn’s total lack of previous knowledge about language education, the app has proved popular, with its 30 million users dispersed nearly equally across North America, Latin America and Europe. He said he hopes the April 24 launch of services in Japan and China will further fuel Duolingo’s growth. He wants it to be the world’s main language-learning tool and is aiming for 150 million users worldwide.

The Japanese-language app, now only available for iPhone and for learning English, will be available in an Android version in about a month and in Chinese and French by the end of the year. The app currently has 275,000 users in Japan, according to von Ahn.

What particularly excites math wizards like von Ahn is that, with 30 million users, he can now use the vast user data to figure out how to better teach a language and get the results reflected in the app in a matter of days — something a typical language teacher with a class of 30 students can only dream of.

“For example, we wanted to know whether we should teach plurals before adjectives or adjectives before plurals,” he said. “For the next 50,000 users who sign up, for 25,000 of them we will teach adjectives before plurals and the other 25,000 (vice versa). And we are going to measure which learns better.”

The results will determine how lessons are provided in the future.

Von Ahn said he wants eventually to offer similar education services in areas other than language, such as computer programming.

“I wanted to work on education because I’ve always had a passion for education, but also because I think in the next 20 years education is going to completely change,” he said, noting that technology will help narrow the existing divide in learning opportunities. “It has to. It’s one of those things that have not been revolutionized by the Internet.”

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