I've recently learned about the
Code:
<dc:language>en</dc:language>
in the content.opf file. Changing it to en-GB made a lot of my UK English books cleaner as far as spell check was concerned
If you change (if necessary) it to
Code:
<dc:language>it</dc:language>
I wonder if it'd make a difference?
http://www.w3schools.com/tags/ref_language_codes.asp