Question about Nintendo Super Mario Odyssey

The game card may be multilingual, but the packaging of Nintendo games is always localised for each country, I know that if I got the German version the game would also be Italian, but the cover would be German...

There is no Italian version. When you first set up the Switch you can set the system language to Italian and automatically all games will also be in Italian. I bought the DE version, but as I just wrote you can set it to your preferred language.