OTL the Nine years war (1594-1603) was a war in which Irish rebels rose against the English monarchy. After they failed many fled to Europe in what became known as the Flight of the Earls.
In this timeline they instead flee to the uncolonised Nova Scotia, inhabited only by the Native Mi'kmaq people. They manage to fight off the raids by later Canadian colonists and, under the protection of the French and, after the American Revolution, Americans they managed to survive as an independent nation to this day. Irish is the majority language, spoken by the vast majority of the population. In the southernmost Cúige (province) of Dún na Mícmigh (Literally meaning "Fort of the Mi'kmaq") Mi'kmaq is also an official language, and the cúige is primarily inhabited by those of Mi'kmaq descent. It is the only monarchy in the new world with a dynasty that doesn't rule any countries in Europe, under the Ó Aodha dynasty founded by Aodh Mór Ó Néil (Hugh O'Neill).
It's existence as an independent, Irish speaking country has inspired many in the Irish mainland, and in times of trouble there many fled to Tír Aodha for peace and safety. When the Irish homeland gained independence in 1921 the re-establishment of the Irish language was made a much higher priority, as a result in the 2022 census it was found that over 80% of the island speaks it as their first language. The two countries have always been extremely close, both culturally and economically. A result of this is that there is a small, yet very vocal, group of people advocating for unification between the two into one Irish nation.
Also placename translations for those interested:
You could talk about how the existence of an Irish speaking country would make the Irish language reforms of the 1920s less likely and different and therefore these translations are wrong ach níl Sean Gaeilge ar bith agam so i dont care.