In a recent interview for the series, its creator, Luis von Ahn, said: "There's an independent study that shows that if you use Duolingo for 34 hours you learn the same as you would in one university semester of language learning".
In fact, according to an independent study conducted by the City University of New York and the University of South Carolina, an average of 34 hours of Duolingo are equivalent to a full university semester of language education.
However this has not been translated into ensuring that the university uptake of languages such as Chinese and Arabic matches Britain's needs.
A number of significant findings – such as the closure of university language departments, less than half of GCSE students studying a language and three-quarters of UK adults being unable to speak any of the 10 most important foreign languages – have brought the country's language issue into sharp focus.
Despite the recent closures of university language departments, there are still plenty of institutions offering courses in the modern classics - French, Spanish, German, Italian - as well as those considered niche a decade a go - Mandarin, Arabic, Japanese, and some of the African languages, such as Swahili.
So few young people are learning languages that in 10 years' time as many as 40% of university language departments are likely to close.
So few young people are choosing a languages degree that in the next decade as many as 40% of university language departments are likely to close.
Chris Hamnet is professor of geography at King's College London In 2006 the Observer published a letter signed by 50 directors of university language centres asking the government to consider making a foreign language compulsory again for 14 to 16 year-olds.
Temple University psychological scientist Kathy Hirsh-Pasek, working with colleagues at several universities, wants to broaden our understanding of language quality by examining what she calls the "communication foundation".
The websites of universities, language schools, school districts and private corporations often list online teaching opportunities in their career sections.
