Hi Randy,
Thanks for your reply.
I don't use any cache plugin and Joomla cache is disabled.
The last time I had the problem, I checked the cookies with a Chrome browser add-on (Edit ThisCookie). I found 4 cookies with language parameter inside. 3 of them had tr-TR and one of them had en-GB language parameter. When I deleted all cookies for the site, problem disappeared. That is why I think cookies cause the problem.
Thank you.
Melih