not directly related: the ALT + click is a system shortcut on linux mint (cinnamon) to drag the whole window :)
is there a way to edit the shortcuts manually (config file, xml, whatever, anything is fine fore me!)

I have a german keyboard layout as well. Could this be the reason a lot of shortcuts don't work or work only occasionally?

for example: 

cmd+p to change resolution doesn't work 

cmd+z / cmd+shift+z only works occasionally

{ and } have a 50/50 chance to work

 backspace to delete a point doesn't work