Problem in date
 

Hi*
My forum's language is Turkish. When I want to enable the date format like Expanded European Format (e.g.* 25th April 1998): jS F Y

it appears in English* I mean "April". I want to change it to in Turkish.
I tried to set an appropriate Locale under Languages & Phrases -> Languages Manager -> Turkish -> Edit Language.

But when I write "trk" or "TR" or "tur"* there is a error:
"The locale 'trk' could not be located on this server for any ."

How can i fix this issue ?

Thanks