My world, Angodena, is very similar in that it's fantasy, it's created in my mind, and there is a totally fictional language that I am busily creating.

I have put down basic grammar rules, and am working on creating a dictionary, and am also trying to sketch out the world with continents and seas and such.

But I force myself to write, even if I don't know, because I can go back and correct eventually, otherwise I'll never write.

Jira is my nickname, yeah, but she's also the main character in this novel and I know her almost better than I know myself, yet she constantly changes as well.

I agree, you just have to write. You can't just keep preparing. At least, I think that's what this post is. If I'm wrong, correct me.