Here's a set of expressions and sample sentences re Christmas and New Year's:
Merry (Happy) Christmas [to you/you all] Nollaig Shona [dhuit / dhaoibh]
Merry (Happy) Christmas to [you/you all]. [response] Nollaig Mhaith [chugat/chugaibh]
Happy (Prosperous) New Year [to you/you all] Athbhliain faoi [shéan 's faoi] mhaise [dhuit / dhaoibh]
The same [to you/you all]. [response] Go mbá hé [dhuit/dhaoibh].
Christmas Nollaig
Christmas time um Nollaig / faoi Nollaig
Christmas Eve Oíche Nollag
Christmas Day Lá Nollag
Christmas Night Oíche Lá Nollag
St Stephen's Day Lá ‘le Stiofáin (Lá Féile Stiofáin)
Wren Dreoilín
Little Christmas Lá Nollag Beag / Nollaig Bheag
Epiphany Lá Chinn / Lá Dá Dhéag
Women’s Christmas Nollaig na mBan
New Year Athbhliain / an Bhliain Úr
New Year’s Eve Oíche Chinn Bhliana
Christmas Pudding Putóg na Nollag
Christmas cake Ciste Nollag
Mince pies Pióga mhionra
Present (gift) Bronntanas / féirín
Christmas stocking Stoca na Nollag
Mistletoe Drualas
Holly Cuileann
Midnight Mass / Birth Mass Aifreann Meán Oíche / Aifreann na Gine
Carol(s) Carúl / carúil
Choir Cór
Manger Mainséar
Candle(s) Coinneal / coinnle
Christmas card(s) Cárta(í) Nollag
Christmas tree Crann na Nollag
Decoration(s) Maisiúchán / maisiúcháin
Father Christmas Daidí (na) Nollag
Snowman Fear sneachta
Bell(s) / Little Bells Clog / cloig / cloigíní
I have written a long letter to Santa Claus. Táim tar éis litir fada a scríobh chuig Daidí (na) Nollag.
Have you finished all your Christmas shopping yet? An bhfuil do shiopadóireacht na Nollag críochnaithe agat fós?
I hope we will have snow at Christmastime. Tá súil agam go mbeidh sneachta againn um Nollaig.
I love to go to Midnight Mass. Is breá liom dul chuig Aifreann Meán Oíche.
I put up the lights and the decorations on the tree. Chuir mé na maisiúcháin agus na soilsí in airde ar an chrann.
We will have a candle in the window on Christmas Eve. Beidh coinneal againn sa bhfuinneog Oíche Nollag....