How far do YOU go when planning a plot?

Do you just get a basic outline, without really getting into too much detail about the background?
For people who write in realistic settings, they don't really need to go into too much detail about a setting that many people are already somewhat familiar with.
But what about fantasy writers?

*cough* mkay, not too many medieval fantasy writers here anyways, amiright?

But say you do come up with a plot set in a different world, at a different time. How far do you go? Do you create ecology? Biology? Certain terms, places, types of people, animals, phrases?

Is it all 'too much' "unnecessary" work to you, or is it something that is a lot of work, but usually worth it in the end?

The reason I bring this up is pretty much just because I want to tell the world that I've successfully created my own language for a book I've been planning for a while now. I'm still planning it, but this is a big leap for me that I'd like to share. Why? Because it takes a long time to do something like this - so much goes into creating "extra" things for a lengthy story and every once in a while you have to try an congratulate yourself after some milestones.

So, here it is, my first song in the Arlithionian language I've created for my book.



I'm not even going to make an excuse for why I can't sing. I just wanted to show that I can do eeet. x)

So, anyways. Opinions on the first topic? How far do you go when creating a backplot for your story and is it even worth it?

~CI

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PS The Arlithionian language was created for the Dreakoni tribes - a race I also created - and is important to both the elements of my plot because of its significance to the deities involved, and to the Dreakoni cultures~