[[Localisation guidelines|Don't customise]]
Hi Nemo, the thing is that, in Portuguese, foreign words should be in italics (just because they are not Portuguese) so, site, link, browser, software, savoir-faire, ex aequo, pari passu, etc, should be in italics. You can see this in living colors here. In many places of MediaWiki it is possible, strings are parsed correctly, and they come out right. In the old days, it was more appropriate to enclose them in <i> tags, just in case they weren't parsed. I did that in the Education Program extension, they literally came as <i> in the interface, so removed them all. I'm not customising the strings or giving them a different meaning, just representing them as they "should". If you see an issue, I can remove all.
I understand this usage of italics for linguistic purposes (it's the same in many languages), I'm just saying that if a term needs to be quoted as is in all translations then we should alter the English message so that the markup works as needed.
As for loanwords, there is rarely universal agreement so I trust you'll be careful. For Wikibase translations, have you checked wikidata:Wikidata:Glossary/pt? I see the term was translated there: .