Answer: Klingon

There are quite a few fictional languages in the realm of sci-fi and fantasy novels, movies, and TV shows. The ancient race of planetary rulers and their servants in the Stargate universe speak Goa’uld, the servants of Mordor in the Lord of the Rings universe speak Black Speech, and inhabitants of Superman’s home world speak, you guessed it, Kryptonian.

Among all the fictional languages out there, however, few languages have captured the interest and imagination of fans in such a way as Klingon has. The Klingon language first appeared in 1979’s Star Trek: The Motion Picture and interest in the language has remained high ever since

In fact The Klingon Dictionary, published in 1985 and then revised and reprinted in 1992, has the distinction of being the world’s best selling fictional language dictionary: it has sold over 300,000 copies and been translated into four languages. Later, it was republished in ebook format in 2008 and a year later in 2009, publisher Simon & Schuster released a digital app version of the dictionary for iOS (as part of three applications rolled into a Klingon Language Suite).

What’s particularly interesting is that the dictionary wasn’t originally intended for public distribution. Mark Okrand, linguist and creative mind behind the Klingon language, created the dictionary to help scriptwriters and actors wrestle with Klingon during the writing and filming process.