This could be thread creep, but Joe Offer has made the point that the Irish had to celebrate Mass in Latin, probably up until the time of the Vatican Council that is usually referred to as Vatican II.

However, if I remember my history (or a version of it!) correctly, one of the reasons the Norman English received Papal permission to invade Ireland was that Rome wanted the independent-minded irish church pulled back into line.

One of the manifestations of Irish church indepoendence could have been celebration of the Mass in the Gaelic/Celtic/Irish language - but I'm on fairly shaky ground here. Does anybody else have any theories?