[otrs] datetime

Hi, I have OTRS 2.0.1 version. I have configured Otrs ; default Charset>>iso-8859-9 Deafult Lnaguage>>tr(turkish) But after I configured these options, I take an error >>>" DateFormat needs to be translated! " on my ticket's "created" tab. So, I cant see my tickets creeated date. How can I resolve this issue? Thanks.