Thank you for your correction and the explanation. Thank you very much.

Depending on the context, "you" can be second person singular or second person plural. So more accurately, English does have a second person plural, but there is no standardized and distinct second person plural pronoun. Also, "you all" is acceptable, especially to make it unambiguous if you are referring to one or multiple people. More formally, one might write "all of you" instead of "you all," but either is okay.

Example: A teacher wanting to get their class to listen could say: "You need to listen up!" But, it is more clear to say: "You all need to listen up!" This way makes it obvious they are referring to the whole class and not just one student. (This could also be "All of you need to listen up!")

I also think "y'all" has a place in spoken English outside of just the US Southern dialect. First, it avoids the ambiguity of only using "you," and "y'all" is much more fluid in speech than "you all." Second, the common phrase "you guys" is gendered, while "y'all" is not. Personally, I use "y'all" even though I don't have a southern accent and have never lived in the South. I would, however, avoid using it in writing.