There are places in the application where it's possible to get a notification containing an exception message straight from the kernel.
1. Go to Admin -> Roles
2. Add a new Role
3. Try to add a new Role with the same name
Error notification with message Argument '$roleCreateStruct' is invalid: Role '8' with the specified identifier 'Marek' already exists is displayed, which is aimed at developers (and not common users, like editors).
It would be good to change the error message to something less confusing for non-technical people.
This also means that the messages cannot be easily translated, making it even harder for non-English users.