Having translated settings names is a bad idea. If user changes GUI language one loses settings. Also settings might be exported/imported and translated names might not work between systems/users.
Threads must be exited from check cleanly even though it takes small amount of time. Just terminating thread can have unpredictable side-effects (even weird crashes).
Items are now hidden from the tree and the tree is not recreated everytime it is refreshed.
Also added test.cpp as a sample data for GUI testing.
Added Check all and uncheck all buttons to menu to show/hide all errors more easily.