One day, I had a wandering brain moment and decided I needed my own language for my stories. I knew right away that it wasn't an elven language, but it was something ancient, forgotten, and tied to magic. I wanted something I could use across various stories in different ways. For example, I have a character who speaks it when he's upset, but in another story, the main character uses it only when performing a spell. It's not the words themselves that are magic; there must be talent and intent behind them or they're just words.
I needed a language that was different, so I used loosely the rules I learned from the linguistics classes I took in college. (Love linguistics, btw. It's algebra for words!) I selected sentence structure, created tense markers, negative markers, placed vowel restrictions on myself, and went to work.
I've got around a dozen phrases and two hundred words, some of which I've yet to designate a meaning. It's good to have extras. I never know what a character's going to say until they say it, so it's nice to have something on hand if I don't already have a translation. And I have a translation! I forget sometimes what they mean myself.
While building my base vocabulary, I discovered another use for my new language: to make my cousin's head hurt. Hehehe.