I fixed it by adding a second system language as turkish, after that i could add the turkish layout and still use english as a default system language.

This is a summary of a common problem on some Linux systems, particularly those using the GNOME desktop environment, where the graphical settings menu doesn't show all available keyboard layouts. The Turkish layout, in this case, is likely installed but not visible in the menu. This issue can be resolved by using a command-line tool like setxkbmap, the gnome-tweaks application for a more permanent solution, or by directly editing the /etc/default/keyboard configuration file to manually add the desired layout alongside the existing English one.