The Klingon Dictionary,which is copyrighted by Pictures, has sold more then 300,000 copies, and has made quite a bit of money for Paramount Pictures. Unlike Esperanto, Klingon is an extremely complicated language with a complex grammar, making it an immensely difficult language to learn. As a result, it is estimated that only a few thousand people can speak Klingon with any fluency. Yet interestingly, Okrand intentionally made Klingon difficult to learn. His goal for Klingon was almost the opposite of Zamenhof's goal for Esperanto. Okrand did not want many people to be able to speak Klingon fluently. On the contrary, Klingon was designed to be and exclusive language that could only be spoken by the most committed Star Trek fans. The vast majority of invented languages have disappeared almost as soon as they were created. While the most successful invented languages, like Esperanto and Klingon, have caught the imagination of a community of people, these languages are spoken more as novelty than as a practical, everyday language. The fact no in vented language has ever become widely spoken seems to tell us something: It languages that evolve naturally and slowly over time that have power to spread, to continue, and to become part of our identity.