I don't think English ever had a second person plural informal. Spanish does:
Singular Plural First Person (I/we) yo nosotros Second Person (you/y'all) Informal tú vosotros Second Person Formal Usted Ustedes Third Person ([s]he/they) el
Admittedly, while the second person singular informal is used quite a bit -- in particular, en famille (to mix languages *G*) -- the second person plural informal is almost never used today. It's my understanding that it's only taught in schools so kids can understand writing of three or four generations ago.