In Dublin and across Ireland, English is the language almost everyone speaks in daily life at school, in shops and basically everywhere. However, Irish (Gaelic) is the first official language of the country. I see it on road signs, official documents and public announcements. Even though it's not widely spoken conversationally, it's a huge part of Ireland's national identity and cultural heritage.
In Dublin and throughout Ireland, the currency used is the euro (€), just like in the rest of the Eurozone. The Eurozone includes the 21 European Union countries (out of 27 total) that have adopted the euro as their currency. In addition to cash, most places in Dublin also take card and contactless payments, including Apple Pay. Coming from the US, I definitely take a second to convert mentally from dollars to euros. Euros are worth more than US dollars, so if I buy an item for 10 euros, it costs about 12 US dollars.
In Dublin, a regular 1.5 L bottle of water at a shop or supermarket usually costs around €1 to €2+ (sometimes less in big supermarkets and more in corner shops and cafes). Smaller bottles can vary more, and prices are often higher at places like airports and restaurants.
