The Irish constitution states that "the Irish language as the national language is the first official language" and "the English language is recognized as a second official language" (Bunreacht na hÉireann, Article 8) . But what is the truth? Irish is in fact a minority language. Despite the best efforts of the state.
The Irish Language
Irish, or gaeilge in Irish, is part of the Gaelic group and one of the still existing Celtic languages in Europe. Other remnants of the Celtic heritage are Gaelic (Scots), Manx, Welsh, Cornish and Breize (spoken in Brittany). Of these Welsh is the most popular, actually being used on a day to day basis in wide parts of Wales.
Old Irish was the lingua franca of Ireland at the time of the Anglo-Norman conquest, then went into a slow decline. Later the language was actively suppressed and English became the main means of communication. Only remote communities, mainly on the west coast, managed to keep a living tradition. This was later documented by scholars, the oral tradition making it into the academic world. And once the academics had re-discovered Irish the nationalists followed, making a revival of the native language part of their program.
Unfortunately Irish had developed into so many dialects that the "revival" was more of a reconstruction, some modern linguists even calling it a reinvention.
After independence was gained the Irish state made Irish the first language - especially de Valera was at the forefront of this movement, trying to undo nearly 800 years of English cultural influences. Special areas were designated as gaeltacht, and in a misguided attempt to spread the Irish language plantations of natives from the west were established in the east. Irish became mandatory in all schools and was for the vast majority of students the first foreign language they learned. To this day all schoolchildren in Ireland have to learn Irish and English, then they graduate to "foreign languages".
In fact either Irish or (in a lesser degree) English is a foreign language to most students. Only in the gaeltacht areas Irish might actually be the mother tongue, for the vast majority of Irish children it is English. The Irish state has, however, committed itself to providing each and every piece of official writing in English and Irish. This is a million-Euro-industry and benefits mainly translators and printers - Irish versions of documents tend to gather dust even in gaeltacht areas.
Statistics differ, but the reality of Irish is depressing for its supporters and laughable for critics - it is estimated that millions of Irish have "knowledge" of Irish, but only significantly less than one percent use it on a daily basis! For the tourist all this might be irrelevant - just be assured that you will not have to speak or understand the "first language" of Ireland, a few essential words of Irish will do.