There's a known issue with tr_TR locale - it will break activeCollab. Reason for the is the change in behavior of some fundamental PHP functions when this locale is applied (strtolower() for example). This is an old PHP bug that haven't been fixed for almost 8 years.
Currently there's no solution, so it's our recommendation that you don't use tr_TR locale. Use any other locale (en_GB for example), but have Turkish translations. Date and time will not be properly localized (it's locale dependent), but everything else in the interface will and that's still far better than having no localization support.
In case you already added tr_TR localization and set Turkish language to be the default language, than go to acx_config_options database table and set the value of "language" to "N;". After that, clean all cch_ files from /cache folder. That will restore the default language to English and make you able to access the setup again.
We'll see if there's something that we can do about this in the upcoming bug fix release.
Currently there's no solution, so it's our recommendation that you don't use tr_TR locale. Use any other locale (en_GB for example), but have Turkish translations. Date and time will not be properly localized (it's locale dependent), but everything else in the interface will and that's still far better than having no localization support.
In case you already added tr_TR localization and set Turkish language to be the default language, than go to acx_config_options database table and set the value of "language" to "N;". After that, clean all cch_ files from /cache folder. That will restore the default language to English and make you able to access the setup again.
We'll see if there's something that we can do about this in the upcoming bug fix release.