By its 10th anniversary this year, the app had been downloaded half a billion times around the world, with 20m UK downloads. Von Ahn became one of Silicon Valley’s leading entrepreneurs, launching Duolingo with his co-founder, Severin Hacker in 2012. It cost me $1,000 just to fly there and take the test. “In my country they ran out of these tests so I had to fly to a neighbouring country, El Salvador – which, in the late 1990s, was a war zone. “I applied to come to the US to study,” Von Ahn told the Observer. These countries include Mali, Niger and more than 20 others in Africa South American countries including Uruguay, Paraguay and Von Ahn’s native country, Guatemala, and many Caribbean and Pacific islands. Yet that leaves people in 67 countries having to travel abroad to take a test.

These are available in 134 countries and territories, according to Home Office data. Currently, visa applicants need to demonstrate their grasp of English by taking a “secure English language test” in an approved centre.

Duolingo test login