Translation:Can you bring a big plate, please?
Lol! Let's talk about a difficulty that can be avoided if one but uses appropriate grammar! A little note for Spanish speakers attempting to learn English, just so you avoid the possibility of difficulties with English speakers. One can accept this as a working translation so long as the questioner does not actually expect to be brought a large plate as a reaction to the question. "Can you bring a large plate", is asking if one is able/equipped to do so, it is not actually a request for a plate. If one wishes to request a plate in English one ought to phrase the request in a way more like, "Would you bring a large plate, please?" Do you see the difference: can/could, and will/would.? Will/would is the better choice in this instance (actually, "would" is preferable as "you will" is an imperative in the second person so saying "will you" might be deemed an offensively imperious statement); otherwise, one might find one's self being answered that one can, or is capable of doing so without the task necessarily being performed. Lols, yes! People do that! Some English speakers are a bit loose with their speech patterns and use the these two terms interchangeably while others do not. Once again, Can you/could you, is merely asking if one is capable of carrying out a task without wanting the task to be performed. "Will you/would you", is actually acceptable word usage for making a polite request which is sure to be understood as such.
Another thing: some English users become quite upset at being asked if he or she "can" do something under certain circumstances. They will interpret the query as a passive/aggressive way of the questioner insinuating that the person who is being questioned is incompetent to perform the given task in question. especially if the task is a simple one. With other English speakers the statement being made just goes right over their heads so no offense is taken. It's best to avoid the possibility of being misunderstood, am I right?
Lols, this is just one of the many little problems one can encounter when translating from one language to another, especially when working with persnickety 'ol English because some are trained to pick up on the nuances of the language and others are either not, or are prone to lapse into more idiomatic varieties of the language where distinctions are ignored.
No. Formality is given by the usage of "usted" instead of "tú" (in the countries where this applies).
Also, the use of the "señor", "señora", "señorita" is not an absolute requirement for formal speech in Spanish (as it may be in English).
The presence of "por favor" just hints/points to formal speech: polite speech normally makes use of formal speech in Latin languages to the point that they are almost indistinguishable (yes, one can be impolite while using formal speech but that's a different topic).
Bottom line, do not apply English language rules to Spanish language (or vice versa).
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.