When fantasy epic Game of Thrones returns for its final series at 2am on Monday not every fan will need to look at the subtitles as Daenerys Targaryen addresses her army of warriors.

Nearly 100,000 people in the UK have signed up to learn the Game of Thrones language High Valyrian on Duolingo, the language learning app – more than the number who understand Scottish Gaelic, which stands at 87,056, according to the last census.

Those fans will now be able to expand their learning with a new version of the course that claims to have enough words for them to be able to conduct a full conversation, even beyond the realms of dragons, queens and eunuchs.

David Peterson, the creator of High Valyrian, has written and voiced the new Duolingo course which launches on Sunday with more than 2,000 words in the official vocabulary. So will fluent High Valyrian speakers be able to strike up a conversation with him?

“Oh no. Absolutely not,” he said. “I’m an academic linguist. I know the grammar very, very well but when it comes to speaking stuff off the cuff – no, I really need practice.”

Peterson is the linguist TV producers go to when they need to add verisimilitude to their fantasy or science fiction shows. He worked on the pilot of HBO’s Game of Thrones, turning the 56 Valyrian words scattered throughout the novels of George RR Martin into a proper language.

The starting point was valar morghulis, a phrase that crops up frequently and means “all men must die”. From there, Peterson built phonology and grammar, going as far as creating loan words from High Valyrian into Dothraki, the language spoken by Daenerys’s horde of nomadic horsemen.

Learning High Valyrian may reward viewers in unexpected ways. In a pivotal scene in series three, Daenerys tricks the owner of the Unsullied slave army into selling them to her in exchange for one of her three dragons. They communicate only through a translator, yet she secretly understands every word and reveals her trick when she tells the slaver – struggling to control his new purchase – that “a dragon is not a slave”.

“It’s my favourite scene,” Peterson said. “She speaks High Valyrian, he speaks Astapori Valyrian. So what I did was I had Daenerys use his word for slave specifically to drive home the point that yes, she understood everything that he’s been saying the entire time. That entire scene hinged on the language. It’s one of the few things that I think is hands down better on the show than it was in the books just because of the way it was executed.” Launching the language into the real world invites people to adapt it, and perhaps invent their own Valyrian words. Peterson says he has no plans to create a High Valyrian equivalent of the Académie française to decide if a word is valid. He prefers the example of Johannes Aavik, who created a dictionary of 2,000 Estonian neologisms in 1919. “These were just brand new words that he made up out of thin air. People started using some and now they’re part of the language.”

Made-up languages go back much further than Aavik, from 13th-century cases of glossolalia – speaking in tongues – to phrases in Thomas More’s Utopia, according to Dr Dimitra Fimi, a lecturer in fantasy and children’s literature at Glasgow University who has written extensively on invented languages. “In the excitement of the Enlightenment, people like [John] Wilkins and [George] Dalgarno tried to create a perfect human language for scientific ideas,” Fimi said. “The problem was these languages were unusable. They tried to define the universe.”



Speaking in tongues



Valyrian (Game of Thrones)

Nuhe averilloma kepe ykynan

I smell my drunk uncle

Quenya (Lord of the Rings)

Elen síla lúmenn’ omentielvo

A star shines on the hour of our meeting

Klingon (Star Trek)

Hab SoSlI’ Quch

Your mother has a smooth forehead

Lapine (Watership Down)

Pelil éan, atha néan

Old legs, young heart

Utopian (Thomas More)

Bargol he maglomi baccan ſoma gymno ſophaon. Agrama gymnoſophon labarembacha bodamilomin

I alone of all nations, without philosophy, have portrayed for mortals the philosophical city