Translation:Can you bring a big plate, please?
Grammar police right? May you bring a big plate, please? was rejected, in favor for Can.
It is not colloquial English to say "May you." Usually, "may" is used when asking for permission, as in "May I ... ." Only then is "may" used in a second person response, as in "You may ... ." It is NOT colloquial English to start a question with "may you."
"Can you ... " is used to ask someone to do something. Because "can" means "are you able to," when a person is asked if they "can" do something the implication is that the have the ability, you know they have the ability, and you are requesting a feat that you know is possible. When native English speakers want to be more polite about the request, they use "could" instead of "can" because conditional tense inherently acknowledges that someone else's compliance with their request is voluntary and gracious.