Hi @Yusif,
This is a very weird known issue with PHP. See http://www.sobstel.org/blog/php-call-to-undefined-method-on-tr-tr-locale/ for details.
To work around it, you’ll need to edit lib/pkp/classes/i18n/PKPLocale.inc.php, find the initialize function, and add this to the end of the function:
if ($locale == 'tr_TR') setlocale(LC_CTYPE, 'en_US');
Regards,
Alec Smecher
Public Knowledge Project Team