Running out if ideas. What happens if (in Windows, not Word) you go to Start > Office > Office>Tools > Office Language Settings and change the Office language to Italian? Amongst other things, it should change the Ribbon to Italian; hopefully it will fix the proofing too. You should then be able to change it back to whatever your current settings are.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

I've already tried that too but it didn't work =(

Ok, thank you very much for trying!