Ireland is one of the places wherein English-speaking people will have no problem with trying to communicate with the locals because the locals will have no trouble understanding English. Aside from English, they also speak Irish Gaelic. In fact, this is considered to be the main language that is used by the people there. 30% of the people in Ireland will know how to speak Irish, but only a few of them will use Irish constantly.
Most of the people there will probably speak in English, especially if they feel that they need it for their line of work. Those who work in the tourism sector would need to know how to speak English properly to communicate with various tourists from different parts of the world.