I know it's churlish to complain since Irish duolingo is a wonderful thing and I'm grateful for all the work that's gone into it and it's something that will improve with use, but:
I wish it wouldn't be so hard on Hiberno-English, it rejects "I amn't" for "I'm not" and "guards" for "police" and "be buying" type constructions in the verbal noun section and even, once, "That's a different story altogether" though thankfully that's been fixed.
Southern English and African American English both use y'all, whereas other American dialects use "You guys". I speak pretty much standard American English, but I use y'all (and some other features of Southern English) because my mother used to live in the South. Also, the fact that English doesn't have a universal pronoun for the 2nd person plural kinda bugs me, since most other languages do. If we don't have a "y'all" (or a "ye", in your case), what's the point in having a "we" or a "they"?
I think you have a point about guard, but would you expect them to accept 'ain't', because it's the same thing? There's a difference between accepting feature of standard Hiberno-English that would be used in normal interactions with people you don't know, or in an email to your boss, and accepting slang that is a feature of spoken rather than written English.