A new project helps people learn a new language by having them translate the Web into Spanish, German, and French.

A fascinating new project from Carnegie Mellon University, called Duolingo, invites language learners to practice their skills while also putting their time to good use by translating real Web pages as they learn.

Duolingo officially launched today after several months of beta testing, and it's a community-centric project that relies on user participation to work. Its language-learning side actually does teach new words, phrases, and some grammar rather effectively and at a pace that's suitable for new learners. But as language learners develop more skills, they can try their hand at translations, which are pulled from real websites in the language being learned. Other users then vote on which translation is most accurate. Eventually, the translated pages, based on the best results, will be published so that more speakers of other languages can read them.

Having tested the service over the course of several months, I can easily say that it's one of only a few free language-learning applications that's actually successful (read my complete for more).

Duolingo was first announced during a TED talk in late 2011 by Luis von Ahn, an assistant professor at Carnegie Mellon and one of the brains behind the project. Von Ahn, however, is best known developing the Captcha, a program that helps differentiate human users online from bots by having them type a series of slightly blurred letters into a box, and its spinoff, reCaptcha.

Similar to Duolingo and its dual-purpose nature, ReCaptcha also has a do-good angle. Its primary purpose is to differentiate humans from bots (same as Captcha), but each question and solution is actually a real-world problem: images of scanned books that optical character recognition software failed to recognize. So as users verify that they are human, they are also helping to put the contents of books online or into digital libraries.

Duolingo is free to use and is available in German, Spanish, and English (for Spanish speakers); French is in beta.