The comma is not needed:
Un gatto non è una persona.

The sentence is a translation of the French, so that one should be changed before changing the Italian one. The best solution is unlinking French-English, anyway :)

I'm not sure. Italian is your mother tongue, I'm sure you can sense that the comma is somewhat artificial in this sentence. As for the French, I couldn't say the same on the comma (it did seem in place, at least for me).

why have you unlinked the French and English ?
the English sentence is an exclamation, so I think the apposition "Un chat, ce" render this well, at least it sounds more natural to me for than the litteral translation "Un chat n'est pas une personne" where we lost the "exclamtiv" feeling.

Well well we can relink them, sysko! Don't worry :P

The Italian sentence can work well with the French one, but it's not a strong exclamation without the !. It's only a serious form which insist on the fact that a CAT (not another thing) is not a person.
Without the comma it is only a general (somehow scientific) affirmation, as "A cat is not a person." or "Un chat n'est pas une personne.".

It's not me who can speak about French, but I think that with the comma and no ! works with Italian, and both with/without the comma and with ! works with English. But it's not up to me.

What I really don't like, it's the lost of punctuation in translations, if it's not needed.