Hi Framus

The word "crack" seems to have come into Ireland from North of England dialect via the North of Ireland where it has always been very common. The absorption into the Irish language (with the spelling "craic", there being no k in Irish!) is quite recent. The "Irish" spelling is now frequently used even when the context is English. I've never heard older native speakers of Irish use the word although the younger generation do so - as they do with quite a few other English words, often applying Irish grammatical rules to them

Regards