philgoddard Nov 5, 2019:

It depends who the document is addressed to. If it's a church writing to a civil registry office, "su illustrísima" seems a bit over the top. And as for translations, "your honor" could refer to a judge, maybe, but "your grace" is for an archbishop or aristocrat.
Either way, I'd probably just translate it as "you".

neilmac Nov 5, 2019:

Hmm I though it'd be "Su Ilustrisimo", but when I looked up the abbreviation, it said "Ilmo."...

Daniel Coria Nov 5, 2019:

S.I. = Su Ilma = Su Ilustrísima S.I. = Su Ilma = Su Ilustrísima = Your Honor / Your Grace

philgoddard Nov 5, 2019:

I'm guessing that's why the asker posted the question. It's some kind of honorific.

neilmac Nov 5, 2019:

Abbreviations Before translating it, I'd like to know what the S.I.stands for.