Can You Learn a Foreign Language for Free? ¡Sí, Se Puede!

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¿$499? ¡Eso es un montón de dinero!

Don't understand that sentence? Would you like to? For $499, you can buy the Rosetta Stone Spanish software package (or a 36-month subscription to Rosetta Stone's (RST) online language training tools), and learn how to translate it. According to the company, its products are: "Proven to work. Guaranteed."

But what if you don't have $499 to invest in learning a new language? Or what if you'd just like to learn Spanish for free? (Or Danish, Dutch, French, German, Irish, Italian or Portuguese, for that matter?)

Well, you're in luck. Turns out, there's an app for that.

Introducing Duolingo

The 2013 Apple iPhone app of the year, Duolingo's self-titled online software program offers English speakers free lessons in each of the above eight languages. (It also offers native speakers of 20 foreign languages a free path to learning English as a second language).

More astounding, this free software program may be more effective at teaching a user a language than America's best four-year private colleges -- which can charge as much as $242 per credit hour for the privilege.

A 2012 study conducted by professors from the City University of New York and the University of South Carolina found that people using Duolingo "with no knowledge of Spanish ... will need on average 34 hours ... of study with Duolingo in order to cover the material for the first college semester." In contrast, with a traditional college semester lasting 14 or more weeks, at three hours' of classroom time per week (language lab time would be extra) a college language class involves a minimum of 42 hours' study.

That works out to a math problem that even liberal arts students should be able to grasp. If the professors' data is right, a course of study with Duolingo would be 19 percent more effective than college study -- but cost as much as $726 less for a semester's worth of learning.

How'd They Do That?

Started by the same man who invented the CAPTCHA system used by Internet sites, Carnegie Mellon professor Luis von Ahn, Duolingo likewise accomplishes two purposes at once.

CAPTCHA helps a website to determine if a user is a human or a "bot," and simultaneously harnesses the "wisdom of crowds" to help decipher unintelligible written text for use in digitizing old books. Similarly, Duolingo has dual purposes. Its main one: It presents foreign language in "game" form, entertaining a student as it teaches, and rewarding the student with virtual "skill points" (basically, bragging rights, but with some value for use in buying virtual goods on the site) along the way.

Now here's the twist: As a student progresses in proficiency, Duolingo notices this and may invite an advanced student to visit a special section of the website dubbed "Immersion."

In "Immersion," students are presented sections of real-life text to translate, drawn from real sources such as the English-language Wikipedia. Students submit their translations for "up or down" votes by other users, and translations deemed most accurate by the crowd may then later be used to translate the English Wikipedia into less-fleshed-out versions of the resource -- Spanish Wikipedia, French Wikipedia, and so on.

When You Win, Everybody Wins

To date, Duolingo's free language learning-cum-massive international translation project has attracted 25 million users to its site. Of these, about 15 percent are using Duolingo online, as opposed to via an app -- and about half of these have progressed far enough to become Immersion contributors, says Gina Gotthilf, head of communications at Duolingo.

Gotthilf says that in an effort to keep the service free, Duolingo also includes translation work for websites such as BuzzFeed and CNN in the Immersion text that users can translate. Duolingo can then sell these translations to such corporate customers, raising funds to keep its project running. At the same time, the "very interesting and very timely" texts provided to it by BuzzFeed and CNN help to keep language lessons interesting for advanced students of Duolingo.

Summing it all up: Duolingo provides effective language training, presents it in an entertaining manner using real-life text involving current events -- and does it all for free. Is this something you can try out for yourself?

¡Sí, se puede!

Motley Fool contributor Rich Smith has no position in any stocks mentioned. The Motley Fool recommends and owns shares of Rosetta Stone. Try any of our Foolish newsletter services free for 30 days. To learn about a group of high-yielding dividend stocks our analysts love, check outour free report.