Almost every major language has a plural you. German uses half a dozen ways to say you plural, including sie, ihr, and euch. In France and French-speaking Quebec, Canada, we tourists can say vous. In Italy, we use voi. In Spain, we politely use usted and ustedes, which come from the archaic vuestra merced. Since the U and the V were once interchangeable, the modern contraction is written Ud or Vds. While vosotros and vos are quite common in Spain, they are rarely used in Latin America. Wherever they go, tourists should not use the singular tu except when talking to children or very close friends.
So what happened to the plural you in English? Blame it on the decline of thee, thou, and ye. As English speakers began to use these words less often, thou became the singular, and Shakespeare wrote, “Where art thou, Romeo?” And the word ye became the plural form: “Gather ye rosebuds while ye may.”
As thou soon lost its popularity in the south of England (although it remains in use in many regional dialects throughout England), at about the same time, ye changed to you.
With the disappearance of thou and ye, we got stuck with you as both singular and plural, Some regional dialects in the U.S. have invented a word to fill the gap. In the South, you all (or y’all), is popular, and we very occasionally hear y’alls. You guys and (in England) you lot are also widely used. Youse and yous are also fairly common in a number of places. Although these plurals are considered slang, or worse, they do make sense. Y’all is quite logical, and yous actually follows the rule whereby we make a plural by simply adding an S to a word. Problem solved.