While most of the folk of the Seven Kingdoms speak English, there are a certain amount of those from foreign lands that speak a whole different language, that doesn't even exist outside of the Game of Thrones world. One such language is that used by the Dothraki, if you'll remember it featured quite heavily in the first season when Daenerys married Khal Drogo and we saw her learning how to speak it herself so she could communicate with him and his tribe.
David Peterson, an accomplished linguist, is the person responsible for creating this language for the TV show. He took the fifty or so words used in the books, analysed their structure and pronunciation and created an order for the language; "The subject was first and then the verb and the object, adjectives would follow the nouns that they modified," Peterson told Salon.
So why was a full language necessary for the show when it wasn't as significant in the books? "Well, the driving force for all of this, and of course the reason I’m even on the project, is Dan Weiss and David Benioff. More than any other show I’ve worked on, they absolutely set the tone for what’s expected of everybody that’s working on it and the vision that they want to achieve. And really what they want to do, visually and style-wise, is two things: They want to have a show that’s as realistic as possible given the fantasy setting, and they want to, as much as they possibly can, realize George R.R. Martin’s vision. So those two things combined really necessitates a full language, and that was in fact why they hired me in the first place."
He also told Salon what his favourite words or expressions were in the language; "I was actually pretty pleased with the translation of one of the George R.R. Martin’s idioms. He came up with “sun of my stars” and “moon of my life” and I really like the way “moon of my life” ended up sounding, which is "Jalan atthirari anni."
Jalan what now? Well if you want to learn how to pronouce that, and all the rest of the lingo of the Dothraki tribe, you can in Peterson's new book; 'Living Language Dothraki: A Conversational Language Course'.