I don't know modern Italian well enough to play comparator.
Anyway same phrases that are not likely to be translated the same (games tend to use quite simple language so it is not impossible, at least in English) is a good start.
Stylistic turns of phrase are another good one -- we all have fairly unique fingerprints in text (read much of what I write and you will find a lot of --, (), not many commas outside of asides and names, probably the occasional semicolon,... as a hanging implication, often me missing out small joining words like if, it, is and such)
Errors is better. Did someone make a grammatical, punctuation... error that is likely to only be a human fault.
People copying databases, code, maps and such is a well known concept here and will provide you many tools and techniques that might allow you to tell things by.
As for what goes afraid I don't know Italian intellectual property courts. While yes in English it would be a derived work or similar unless SE sued you and obtained or you otherwise gave them the rights to use it they would have still wronged you in using such things. With that in mind then courts tend not to like things that don't end in monetary awards or jailtime. Moral victory in the press against either Square Enix or their Italian translators is an option though.