"They speak Irish in the Irish speaking area."
Translation:Labhraíonn siad Gaeilge sa Ghaeltacht.
Some replies have mentioned that the definite article is only used for "general statements" about languages... but of course this looks at first glance like a general statement.
However, based on similar sentences in other exercises, I'd guess this is (counterintuitively) referring to some specific people (eg "Pól and Máire speak Irish in the Gaeltacht"). In English the natural interpretation of this sentence is a general statement where "they" implicitly refers to "the people in the Gaeltacht", but in Irish that would be more likely to be expressed with a passive.
but in Irish that would be more likely to be expressed with a passive.
In Irish it would be expressed with the saorbhriathar - labhraítear an Ghaeilge sa Ghaeltacht.
The saorbhriathar isn't actually in the passive voice, but it is usually translated into the passive voice in English ("Irish is spoken in the Gaetacht"), because that's how you avoid mentioning the agent in English.
Since there's been no help on this from the experts, I'll cite the Christian Brothers Grammar (par 7.14): that in normal usage, languages don't take an article. But "nuair atá a bhrí forleathan" (when the sense is general), the article may be added. Example: "Is í an Ghaeilge teanga ár sinsear". In the case here, I suppose we are talking about a specific Irish spoken in the Gaeltacht. Whereas when talking of our ancestors, they spoke Irish in a 'general' sense (over centuries, in different areas and in different dialects). Whatever this 'general sense' may mean in practice, there's a nuance of meaning involved which I guess will become clearer with practice.