In a ferociously competitive market for technology talent, Luis von Ahn faces an extra challenge: how to persuade potential staff to move to Pittsburgh, an industrial city in Pennsylvania, more than 2,500 miles from Silicon Valley.

Mr Von Ahn, 40, is chief executive of Duolingo, the world’s most popular language learning app, with 200m users. He co-founded the business seven years ago with Severin Hacker, a PhD student with whom he was working on translation apps, and who is now the company’s chief technology officer. With a background in computer science and cryptography, Mr Von Ahn won a prestigious MacArthur Foundation fellowship in 2006. He is still a consulting professor at Carnegie Mellon University.

In 2011, Pittsburgh had little to recommend it as a centre for tech. It first boomed as a steelmaking hub at the heart of the rust belt but, after the collapse of the steel industry in the 1980s, its population dropped by almost a third.