[Typo3] default language -where to set it?

[T.Joga]

Where I can set default language for typo3?

I am trying to make multilanguage, one tree system. All pages are not 
translated to english, so I have a probleme of somekind. If I ever get 
started thought..

Backend language can still be english. I just want that when I create a 
new page - its content is in my default language - which is not english.

Thanks!
(sorry for a newbie question like this)