My father, who is Irish, is angry about many post-Vatican II changes. One change is that, at least according to him, the traditional Irish saints such as Patrick, Colmcille, Brendan, and the rest, are no longer to be considered saints. The only formally canonized Irish saint (unless there have been some recent ones) is Oliver Plunkett. It is my understanding that there used to be a thing called “popular canonization.” I know that “saint” basically means someone that is in heaven, but are any of the traditional Irish saints “saints” in the sense of holy persons deserving of veneration? The answer to this question might mean a lot to my father.
Your father has misunderstood what happened with the reorganization of the liturgical calendar. Saints were not “dropped” or no longer considered saints; it is simply that some saints had their feast days removed from the universal calendar. (The universal calendar is the calendar of feast days binding throughout the Roman Catholic Church.) Your father may rest assured that his favorite Irish saints are still saints, even if their feast days are no longer universally celebrated.
St. Oliver Plunkett is the only officially-canonized Irish saint of whom I am aware, but others of Irish origin are on the road to canonization. Among them are the Venerable Matt Talbot, who was a recovering alcoholic, and Servant of God Frank Duff, founder of the Legion of Mary. I recommend the article linked below for your father.
Why We Should Be Joyful Catholics** by Joanna Bogle