"They are evil."
Translation:Oni są źli.
"One są złe" = They (only women) are evil. Well, there is a possibility that this "one" describes some other 'not masculine-personal' noun (most probably some animals), but that would rather be specified, we don't usually use the pronouns in Nominative to mean something else than people.
"Oni są źli" (Ź, with the 'accent' and the 'normal' L) = They (at least one man among them) are evil.
Quite ironic. The word used to describe multiple people in Polish looks the same as the word use to describe a singular person (or object) in English.
I'm sure others have noticed this, though, so it's not like a huge breakthrough or anything. Just something that I find amusing, in a weird way.
Well... on one hand, yes, I guess. But that's a veeery specific translation. (translations from Polish Wiktionary: vile, ignoble, iniquitous, wicked, knavish, dishonorable) And as you wrote, 'used in the scriptures'. It's not a word you are likely to hear in an everyday conversation. You would be understood, yes, but people could be a bit surprised. And I'm pretty sure that no one before you has ever suggested it. Given that the word "zły" is introduced so early in the course, I think it would be rather problematic if someone got such a suggested answer, than helpful.
P.S. Yeah, I suppose you are either Polish or know Polish well, but other people will read this answer as well ;)
You'd just say "Są złe", then. In theory "One są złe", but in fact Polish almost never uses "one" for anything else than a group of women.
Maybe "To" can be used for plural objects (To są talerze = These are plates), but if used with adjectives, it could only be singular (To jest złe). So no, that won't work.
There are two plurals: virile (masculine personal plural), which is used for 'groups with at least one man'; and nonvirile (not masculine-personal plural), which is used for all other plurals.
So "oni" is virile (at least one guy among 'them'), and "one" is nonvirile ('they' are only women). Similarly, "źli" is virile and "złe" is nonvirile. So basically, "one" and "źli" don't match each other. It's either "Oni są źli" or "One są złe".