See the bottom of the post for some interesting reflections on the language from Quora.
As far as I can piece together, this Christmas hymn, which does not mention Brigit at all, could perhaps have been written by Bishop Moel Brigid (or Brigidian O'Brolcan), who died in 1097. (Not to be confused with Bishop Moel Brigid ((also nicknamed Brigidian)) who died in 1042.)* Which would make it of interest because of the name, very similar to my own and meaning "Devotee of Brigit."** It is interesting to know there is a "nickname" for Mael Brigde.
More likely, it is simply that the hymn is written in the "Brigidian" language, or presumably dialect. I am at a loss as to what is going on here. I have found a couple of references to it online, but not much. One is a plea for information posted in 2003 and never answered:
"I think that this language was made up, but you never know. Supposedly, it is, or was, spoken in western Ireland."
Brigidian (western Ireland) Boche'
Nóçhé' Nóël, Nóçhé' Cúna / Silent Night / Stille Nacht (Western Ireland Brigidian Version)***
This response on Quora is interesting. There are some other answers that are good, as well.
*Source: Journal of the Royal Society of Antiquaries of Ireland, Vol. I, Fifth Series, Vol. XXI, Consecutive Series 1890-1891, (1892), pg. 518.
** To learn more about the name, go here.
*** Source: Gaelic Rosary Prayers (2011). Bit of a misnomer there.
Image: "Erin makes a Christmas pudding marked 'Home Rule', while Pat brings international support as ingredients,"by John Fergus O'Hea [Public domain], via Wikimedia Commons.
Admittedly, this image has nothing to do with the post, but when I looked for an Irish Christmas image on Wikimedia, this came up, and I thought it was too cool to pass by.