When writing my own stories some of which are fast approaching novel length I have to sometimes come up with languages, I use latin as a huge influence also sometimes greek, russian and norse can come in to it. Other languages are just a major mess about with grammar structure and letter formation.

I also once sat there with 2 friends on a bus just making up a language based on how goldfish open their mouths to breathe in water. This language by the end of our 50 minute journey was completely formed and we could actually understand each other in it to an extent (the rest we guessed at based on body language) sadly I don't speak to either of the people who first made the language now but I have used that language in a very cheesy but successful chat up line (the only one I have used where I have had 100% success rate with it).

The only thing with languages is that you gotta make sure you understand it's grammar structure all to often writers will try making a language only to break the grammar rules of their own language and fall flat on their face when trying to convince the reader it is a language.