The paragraph below,copied from the Wikipedia article mentioned in my previous post explains how the word took the Irish spelling in Ireland
Crack was borrowed into the Irish language with the Gaelicized spelling craic. It has been used in Irish since at least 1968, and was popularised in the catchphrase Beidh ceol, caint agus craic againn ("We'll have music, chat and craic"), used by Seán Bán Breathnach for his Irish-language chatshow SBB ina Shuí, broadcast on RTÉ from 1976 to 1982. The Irish spelling was soon reborrowed into English, and is attested in publications from the 1970s and 1980s. Craic has also been used in Scottish Gaelic since at least the early 1990s, though it is unknown if it was borrowed directly from Irish or from English.