In addition to all the usual phonology, grammar, and vocabulary one has to learn for a new language there is the social situation, among many things when is it appropriate to speak in one register or another. And every language/variety has its own particular social situation to deal with.
Irish Gaelic in Ireland has an interesting past. It was once a classic learned language during the Middle Ages, but declined in use during English colonization and was literally marginalized (to the western edges of the island) by the early 20th century.
There seems to be nowadays two versions of the prevalence of Irish Gaelic in Ireland. One is that the daily users of Irish are still only in this Gaeltacht area (on the western coast). There has been nominal teaching of the subject in school since independence, but few (10%) use it in the home, and even fewer (1%) use it regularly outside the home. Almost everyone speaks English natively in Ireland (even the Gaeltacht Irish speakers), but few speak Irish natively. The default is English.
The other impression is that school teaching over the last hundred years has revived the language, not to the extent of Hebrew in Israel, but to a useful language that many people use. Roads and signs over the country are bilingual, there are newspapers, radio, and television produced in Irish, and what's more telling is that the radio and TV interview national leaders and people on the street in Irish.
These aren't necessarily facts, just a compilation of what I think I've read.
As an outsider, it's hard to judge what's real. Are the TV people selecting the extremely small minority of Irish speakers to interview, are they all using dysfluent grade-school Irish, or are there lots and lots of fluent professionals and everyday people? Are the maps with Gaelic speakers only on the west coast out of date or labeled wrongly?
Is there a better source to justify any a judgement than the wikipedia article on the Irish language?