While Ireland was never really united into a consistent, stable polity in the Middle Ages, there were occasional high kings of Ireland and I was wondering if there is any evidence as to what the other monarchies of Europe thought of them? Would they have been considered equal, at least in rank, to other kings? Would they have had similar educations and spoken similar ‘diplomatic’ languages as other courts?
Well in England they weren't consider equal from 1066 on wards as the Normans considered they ruled all of the British Isles. Henry II got permission of the Pope to conquer the island, I think claiming that it was lawless and unruly. Edward I also had the Scottish claimants swear vassalage to him during their crisis when they had no king.