if nationais is an adjective, the answer could also be "if possible, national" because the sentence does not specify what noun the word "nationais" is referring to.

What does this mean? I don't get it at all.

Remember portuguese is still in beta, if you see a problem report it.

Could "domestic ones" be an applicable translation for "nationais" in this sentence?

this one is confusing

"Nationals" in this sense makes no sense in English. Unless we're talking BE?

This makes no sense without some context.