Claire,

The fancy technical term to sling about in the liner notes is "macaronic". As in, "This lovely macaronic song combines both Irish and English lyrics..." The term applies to any song or poem incorporating any two (or more?) languages.

I'm not getting any results on a Mudcat forum search; I think it's trouble with the search engine. But here's a substantial thread that came up with a filter on thread titles: Macarónachas / Macaronic Songs. Language mixi.

I did a Google search on "Irish macaronic song" and came up with a lot of hits (often from other people's liner notes or reviews). Here are a few:

http://homepage.tinet.ie/~fidil/Companion.html: "Ó Muirithe, Diarmuid has lectured in Irish at UCD, has published on dialectology, his major research being on the macaronic song."

http://www.artslift.org/EN/Projects/SeaSongs/musicologicalThemes/Ireland/irelandSeaSongs.htm
"Broadly speaking the repertoire of the Irish song tradition can be divided into five categories, songs in Irish in the sean nos style, Anglo - Irish songs, macaronic songs (songs in both England [English] and Irish), songs of British origin, and others."

See the notes at the bottom of this page for an interesting related thought on the source of nonsense syllables: http://mysongbook.de/msb/songs/w/whoputth.html
~ Becky in Tucson (as you know!)