For over two thousand years, Ireland has been a host to a surprising variety of languages and cultures: Irish Gaelic, English, French, German, Ulster Scots, Ancient Greek and Latin.
Nowadays most people speak Irish English, or like some claim, English with an Irish accent. A minority still speaks Irish Gaelic, one of the six Gaelic left forms of language. About 30% of the population is able to speak Irish Gaelic.

When you arrive in Ireland, you should know some typical Irish phrases. A good place to start:

Irish language

In this website one finds conversational Irish survival phrases:

Excellent page on the Irish language, many topics with words and phrases