I thought that adjectives in English work in the singular form.
They are not Brazilian.
Here Brazilians is a plural noun, you are right that the adjective version would not have the "s". I'm not sure why they changed from adjective to noun in the translation.
зачем вы рядитесь в чужую шляпку
"They are not Brazilian" was accepted for me (but knowing Duo, that doesn't necessarily mean it was right).
But I am. =)
And in love with Romanian culture since I was a child.
Onde o rio Beberibe se junta com o Capibaribe pra formarem o oceano Atlántico, aí está o Recife. Kkkk