Dear Paul ~ I would say their chances of speaking Irish as their mother tongue were 100%. We have family still in Donegal, and although English is the language they all speak, they are striving hard to preserve the Irish language through their schools. My husband's people are all of Irish descent. They all spoke Irish, including his grandparents, who immigrated in the early 1920's. By the way, the folks in Ireland we personally know prefer their language to be called Irish, not Gaelic. Sincerely, Tamy in Nevada, USA