"Are you a woman?"

Translation: Menyw dych chi?

[susanescott]

It might be asking if a girl is an adult or not.

[pablopublico]

Menyw, a variant of benyw, is cognate with English queen, Norwegian kvinne ("woman"), Ancient Greek γῠνή (gunḗ, whence English gynecologist), Russian жена́ (žená, "wife") and Sanskrit जनि (jáni, "woman, wife; birth; mother; birthplace").

[AilawilHathaway]

Does this sound as rude in Welsh as it does in English?

[rmcode]

That's a very good question. We might need to delete this sentence.

Although I could think of a not too rude context given that popular names like Ceri and Celyn are non gender specific so someone in androgynous clothes with a neutral voice or over the phone might elicit such an enquiry.

[Julianbark6]

Or online, where a name like "rmcode" gives no clue.

[Beth743129]

Would it be correct to use "ydych" in this sentence?

[ibisc]

Yes, and it is an accepted answer.