and a closely related language, Irish Gaelic
https://maynoothcollege.ie/files/images/O%C3%ADche-Chi%C3%BAin-PDF.pdf
"While clearly there were, and are, alternative versions of the carol being sung in homes and in communities across Ireland, it would appear that the version we now recognise and sing as the Irish version of this carol was first printed in January 1939 in the Irish Press newspaper,credited to the Irish writer Tadhg Ó Donnchadha, also known as‘Torna’". [modern spellings added in brackets]

Oidhche chiúin, oidhche Mhic Dé,
Cách ’na suan, dís araon,
Dís is dílse ag faire le spéis
Naoidhean bheag gnaoi-gheal cheannann tais chaomh, [naíon]
Críost, ’na chodladh go séimh,
Críost, ’na chodladh go séimh.

Oidhche chiúin, oidhche Mhic Dé,
Aodhairí ar dtúis chuala ’n scéal [Aoiri ar dtús]
Aililiúiá aingeal ag glaodhach,
Cantain tsuairc i ngar is i gcéin:
Críost an Slánuightheoir féin,
Críost an Slánuightheoir féin [slánaitheoir]

Oidhche chiúin, oidhche Mhic Dé,
Mac Dé bhí gáire a bhéil,
Tuar dá rádh ’s dá lánchur i gcéill [rá]
Ann gur tháinig tráth chinn an tséin
Críost ’sa theacht ar an saoghal, [saol]
Críost ’sa theacht ar an saoghal.