Suairc Nollaig!
Nollaig chridheil agus Bliadhna mhath ùr!
Nodlaig mhaith chugnat!
Nadelik looan na looan blethen noweth!
Nadolig Llawen!
Nollick ghennal as blein vie noa!
Nollaig Shona Dhuit!
Nollaig chridheil huibh!
I'm pretty sure I covered all possible celtic language and particular celtic "way" of joy.
At any rate...my personal wish for all here is
Slàinte mhòr agus a h-uile beannachd duibh.
(Great health and every good blessing to you.)
May your winter festivals bring joyous and good tidings and with the new year all your dreams may come.