Two languages built from a handful of words

The novels contain fragments — a few dozen Dothraki words, a scattering of Valyrian, mostly names and curses. That is not enough to shoot a scene in. The producers ran a competition through the Language Creation Society and hired David J. Peterson, who built Dothraki and the Valyrian languages into working systems with grammar, inflection and vocabulary large enough for real dialogue. The practical test of a constructed language is whether an actor can perform in it rather than recite it, and that requires the language to be consistent enough for stress and rhythm to fall naturally. Two moments in the show turn on this directly: Daenerys revealing in Astapor that she has understood High Valyrian the whole time, and a single word — dracarys — carrying an entire scene. Neither lands if the language underneath is decoration.