In IDLE, with an Italian keyboard, it's impossible to
dedent the text without using the menu, because the
shortcut Ctrl+] cannot be typed. In fact,  with an
Italian keybaord, the ] is typed with Ctrl+Alt++. While
indent can be achieved with Tab, so that's no problem,
dedent is only accesible from menu: I suggest you to
shortcut it as Shift+Tab too, like many other IDEs.

Thank you
Ignazio