Welcome Serkan, as you stated, DNN core has critical bugs when used with computers that uses Turkish in their Regional Settings and it makes database conflicts.
To workaround i had to use Latin1_General_CI_AS as both database and server collation.
Do you have programming knowledge? I tried to open some discussions in Bug Tracker (support.dotnetnuke.com), but Core Team said that it won't be easy to re-organize db creating scripts.
Most of Turkish located DataCenters use Turkish Collations as server collation, when DNN configured to use this collation does not work as expected, it fails even with Latin1_General_CI_AS as well.
The only workaround i had found is using same collation for server and database (both has to be at least Latin1_General_CI_AS) Maybe other collations would work too, but i could not apply any other solution.