"You are women, not men."

It's an irregular noun.

ma (with the umlaut) nner is the plural form of "man" in german not norwegian

"They" translates to "de" in Norwegian, and is not synonymous with the plural "you".

Since the English sentence is ambiguous, both the singular ("du") and plural ("dere") version is accepted in Norwegian.

Since it uses plural nouns, it doesn't need "you all" for "you" to be interpreted as plural.

"De" (always capitalised) is a now obsolete "høflighetsform" for the singular you. We neither teach nor accept it, as it's no longer in regular use.

You might encounter the formal second person singular/plural "De", object form "Dem" (note it is always written with a capital letter) if you watch films and tv from the early eighties or older, or set in older times, or spoken by older people. I still learnt how to use it in school, and it was still considered standard in business correspondence well into the Nineties.

While not current Norwegian, it is useful to know about.

You in English is ambiguous. It can mean both you singular and you plural. But together with a plural noun, it is plural. In Norwegian, we differentiate second person pronouns between singular "du" and plural "dere". Since it says "women", plural, in Norwegian "kvinner", also plural, the pronoun therefore has to be plural "dere". Compare: Du er kvinne, ikke mann. (singular - "entall" in Norwegian) Dere er kvinner, ikke menn. (plural - "flertall" in Norwegian)

"Du" is the singular "you", so it doesn't go with the plural "woman" and "men"

"Dere er kvinner..." but "Du er (en) kvinne...".