What do Game of Thrones' Dothraki, Avatar's Na'vi, Star Trek's Klingon and LOTR's Elvish have in common? They are all fantasy constructed languages, or conlangs. Conlangs have all the delicious complexities of real languages: a high volume of words, grammar rules, and room for messiness and evolution. John McWhorter explains why these invented languages captivate fans long past the rolling credits. [5:20]