Learn what you need to know about the difference between Gaelic, Goidelic, and Gaeilge. Getting language names right isn't just a way of showing respect; it's also critical to being understood.
Most language learners adapt readily to the idea of translation, learning to use new, unusual words for labeling familiar objects. Going from the English language to Irish, “Table" becomes “bord," newspaper becomes “nuachtán," and so on.
For those who aren't particularly dedicated to learning another language, however, or who might be just a little confused, things sometimes run together. For some American English speakers, the word “Gaelic" means an ancient language now spoken with distinct versions in Ireland and Scotland, both members of the Goidelic language family. But the truth isn't so clear cut. Although some would argue that the term "Gaelic" is more properly applied to the Scottish language than to the native speech of Ireland, others shrug, smile, and say the languages are so closely related that it hardly makes a difference. The one thing you can be sure of is that the Irish language has a name for itself: Gaeilge.
Excuse Me, Do You Speak Gaelic?
So when you try to ask if someone speaks Irish you shouldn't say, “Labhrainn Gaelic?" or even "Labhrainn Irish?" No, instead you say, “Gabh mo leithscéal, (excuse me), labhrainn Gaeilge?" Or, for the anti-climactic effect, you can simply sidle up and ask, "Excuse me, do you mind if I try a few words of Irish on you?" Odds are the person you're talking to speaks English, anyway.
Will you get your head taken off if you use the wrong word for a language? Not necessarily, but given that language is a cornerstone of national identify and pride, making sure to get the language name right is just one more way of showing respect--and getting understood. When speaking Irish, it's clearly Gaeilge; when speaking English, your odds are best if you simply call it Irish. Although many will understand if you use the word "Gaelic," you've got good odds of being misinterpreted to mean Scots Gaelic. To make matters worse, the two languages sound enough alike that the uneducated ear would have trouble telling them apart.
Getting language names right is also an important survival skill. In the Irish language, the word for English is “Béarla." While your odds of landing in a room where nobody knows what the word “English" means in Ireland are incredibly slim, it could happen. If you ask for Béarla instead of English, those who don't speak it will still understand what you're talking about -- and if you recognize the word, you might be able to pick it out of a conversation if somebody asks Labhrainn Béarla?, or "Do you speak English?" to have a bit of fun at your expense.
In general, learning critical survival phrases such as "Do you speak English?" in a host country's language is also a good way of showing that you've made at least the minimum effort to facilitate communication... and being able to get yourself out of trouble in a pinch. Again, your odds of ending up in a foreign-language survival situation in Ireland are next to nothing. But trying out a few words in the local language is still a way of showing interest, and could start an interesting conversation.