LILLE, March 23 — From Dothraki and Valyrian in Game of Thrones to the Chakobsa desert tongue in Dune, American couple David and Jessie Peterson have devised numerous imaginary languages — apparently the only two people in the world who earn a living concocting fantasy grammar and vocabulary for film characters.

Immortal lines from the Game of Thrones scripts such as: “You are my last hope, blood of my blood,” plunge viewers deeper into the series’ fantastical world when uttered in the original Dothraki: “Yer athzalar nakhoki anni, zhey qoy qoyi.”