My translation was also accepted by DL: "She did not hear what you spoke ABOUT yesterday."
I had no choice. The given translation is not correct English.
She hasn't heard what you said yesterday ....... or.... She didn't hear what you said yesterday........ both make perfect sense; unlike the supposedly correct answer on offer above!
In English we wouldn't use the present perfect for this sentence, but your second option is correct.
Does Romanian distinguish between speak and say?
Yes. To speak is "a vorbi" while to say is "a spune"
... what you spoke about or what you said. "What you spoke" makes no sense here.
Your given translation is not acceptable English.
Why "voi"? And why no "despre"?
"Voi" is not really necessary indeed once you say "ați vorbit". "Despre ce ați vorbit" would refer to the content of the conversation while "ce ați vorbit " is the conversation itself
The English is crap once again.
ati vorbit = have said or talked about (have talked about). So I used it in my translation and I think it should be accepted to say the least as another translation. Finally what about was said yesterday?
"What was said yesterday" = "ce s-a spus ieri "