May I suggest that Duolingo accept ye, youse, y'all, you'uns, yinn, and all the other words learners suggest? It should be obvious that we NEED a plural you in English! (Yeah, yeah, yeah, I know that You IS the plural form--bring back thou!)
I've been regulally using y'all for sibh (regularly being defined as whenever I have the patience to deal with getting marked wrong and reporting), and about as regularly getting "We now accept this" emails. Nature of the beast, but we're getting there.