The world is full of strange, secret languages that people make up - sending messages coded in Pig Latin or Morse code for an extra level of privacy. Maybe even American English if they really want to confuse people.
And in the same way, making up entirely new worlds populated by strange species and miraculous creatures isn't quite enough for filmmakers, taking it one step further to embellish an entirely new language for their weird-looking beasties that only the most committed of fans will endeavour to learn. Don't want to embarrass yourself at Games Workshop for not knowing the latest Elvish, of course.
Adding wonderfully diverse layers to fantasy lands and far-reaching galaxies, these films and TV shows created a special kind of communication that can actually be applied to real life - fleshing out fully realised native tongues you can actually learn and speak in. Whether it's channeling the dark lord in the Parseltongue of Harry Potter or insulting trekkies the world over in Klingon, there’s directors out there who’ve made something for everyone, if only to REALLY prove your fandom.
Hab SoSlI' Quch, my dudes.