With new mobile app, Duolingo helps you learn languages on the go

Duolingo’s iPhone app just replaced Scrabble as my go-to mobile time-killer. The startup, which was created by Recaptcha founder and Carnegie Mellon professor Luis von Ahn, launched a Web service this summer that helps people learn languages while also translating real-world content from the web. On Tuesday, it announced that it had landed on mobile with a free iPhone (s AAPL) app.

The app mirrors the website with skill-based, game-like lessons, but they’re optimized for a smaller screen and compressed chunks of available time. Each lesson is a bit shorter – so they’re easier to consume while you’re waiting at the dentist’s office or during other little breaks – and they require less typing, so you can progress quickly without a proper keyboard.

I’m only four days and six lessons into it (I can just barely say that I drink wine and read the newspaper in Spanish). But I’m getting hooked. The lessons are quick enough that they don’t feel onerous, but they’re repetitive enough that I remember the content. And, so far, the daily email reminders are keeping me on track.

There are plenty of other (free and paid) language-learning mobile and web apps out there (in addition to the higher-end Rosetta Stone-type programs).  And those trying to learn a language for a specific event or trip might need a program that can move them along more quickly. But, for a casual student looking for a meaningful way to use down time, Duolingo’s app is a great option.

Not only is it free but, as you learn, you can take a small bit of pride in knowing that you’re helping to translate content on the web. In addition to lessons, the platform serves up real-world (skill level-appropriate) content for users to translate and then asks them to vote on the translations of others. Most of the sentences I was invited to translate were way beyond my skill level, but it was still interesting and helpful (and somewhat motivating) to see richer language along with other users’ translations.

“Even if you’re a beginner, after about 15 minutes, things we present to you are from the real world,” von Ahn told me, adding that about 60 percent of the platform’s 300,000 active users translate and learn on a regular basis.

One missing feature on this version of the iPhone app is the ability to record yourself actually speaking the language, but von Ahn said version two will include that capability. Another drawback is the inability to use the app when you’re not connected to the internet (otherwise it would be a perfect commute companion).

For now, the app offers lessons in Spanish, French, German and Portuguese (in beta) but von Ahn said Italian and Chinese are coming soon.

In September, Duolingo announced that it had raised $15 million in a Series B round led by New Enterprise Associates. Last year, the company raised $3.3 million from Union Square Ventures and others.