Emillia Clarke in Game of Thrones as Daenerys Targaryen, one of the characters who speaks High Valyrian, a language becoming popular on the Duolingo app

French is passé and German ersatz: thousands of people are becoming fluent in dead, niche or fantasy dialects such as Latin and Klingon.

While traditional languages such as Spanish and Mandarin remain popular choices for travel or business purposes, hundreds of thousands of people are getting their tongues around High Valyrian, spoken in the television hit Game of Thrones.

The number of people learning Latin via the Duolingo app has reached one million, six months after it became available. And five times as many people are learning Scottish Gaelic as the number of fluent native speakers, 300,000 compared with 60,000, with the biggest proportion in the US. The language is on track to overtake Klingon, from Star Trek, which has 316,000 learners.

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