Originally Posted by
nigel-harps1954
You wouldn't technically be wrong in saying Tuaisceart Éireann as a literal translation of both words, but it would be almost gramatically wrong follow Tuaisceart simply with Éireann. I'd have said you would follow it with 'ná hÉireann' as said already, although that leaves it literally translated as North of Ireland rather than Northern Ireland.
There's a number of ways of saying it, as there are with pretty much everything in Irish. But such are the rules of the language, you're never going to be right or wrong, just what is understood.
As Tets says, Tuaisceart is simply the noun. Your adjective in this case would be Tuaisceartach: 'an Tuaisceartach' - The North.