I admit to my comments re Rathlin Island being a bit tongue in cheek, but there are quite big differences in grammatical construction, preferred ways of expressing ideas, and pronunciation of individual words between and within dialects and accents. In the soap opera Ros na Rún there are three versions of the dialogue to follow - the English subtitled “version”, Irish subtitles, and then what is actually said/spoken by the actors!
If you use the pronunciation files for words available in the excellent online dictionaries you will find that some few but significant words are so differently pronounced between Ulster, Munster and Connaught dialects as to be very hard to recognise/reconcile.
I found it hard, being taught as I was by Mayo man (a dialect/accent not a million miles from Ulster), that when using an Ulster dialect audio-visual course I became unsure how to decide how to “choose a pronunciation” for the ‘reading voice in my head’ (so to speak). I’m still somewhat confused...
The youngsters from all over Ireland going to “Lurgan summer college” in Connemara can get access to an orientation course (Coláiste Lurgan’s Oide app - even you can sign in as as a guest and try it out) in advance of going there to that part of Connemara where they’ll be staying with local families, to attune their ears to the local ‘blas’. That blas/their own local flavour means a lot to many population-wise fragile communities within a Gaeltacht. Some feel that school-taught Irish runs rough-shod over genuine Irish as spoken by native speakers, which does/did still abound in local variation and codes.
Hochdeutsch and Platt is an interesting analogy, but the Irish equivalent to Hochdeutsch, the CO has a much shorter history, being a 20th Century invention, I think. I must admit that all the above is my impression as a beginner to intermediate learner, and I am certainly no expert!