Here are a few seasonal greetings/expressions in Scottish Gaelic (Gàidhlig). For holiday greetings, expressions, and songs in Irish (Gaeilge), see the Irish section of the forum. This thread is locked, because it was getting spammed. If you have additional greetings to add, start a separate thread and I'll merge them in if they fit the theme.

Nollaig Chridheil - Merry Christmas
Nollaig shona - Merry Christmas
Agus a leithid cheudna dhut - Same to you

Oidhche na Nollaig - Christmas Eve
[Là / Latha] na Nollaig - Christmas Day
air an Nollaig - at Christmas
craobh (na) Nollaig - Christmas tree
loinnearan Nollaige - Christmas decoration
cairt Nollaig - Christmas card
Bodach na Nollaige - Santa Claus

Bliadhna Mhath Ùr / Bliadhna Ùr Mhath - Happy New Year
Le gach deagh dhùrachd airson a Bhliadhna Ùir - With best wishes for the New Year
Oidche Challainn - New Year's Eve
Callainn / Latha na Bliadhna Ùire - New Year's Day
Nollaig Bheag - Little Christmas

Latha nan Trì Righ - Epiphany [Three King's Day]
Latha Fhèill nan Righ - Epiphany
Fèill an Taisbeanaidh - Epiphany

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

Time to bump this up and sticky it for the season.

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.