The original song was in Spanish. Christy sings English verses and tells of men like Frank Ryan who went from Ireland to fight against Facism. So if Christy claims authorship, I suppose he did write those English verses in 1983 as he says he did.

Viva la Quince Brigada
Rhum-ba-la, Rhum-ba-la, Rhum-ba-la
Viva la Quince Brigada
Rhum-ba-la, Rhum-ba-la, Rhum-ba-la

Que seha cubierta de gloria
Ay Manuela, ay Manuela

Luchamos contra los Morros
Rhum-ba-la, Rhum-ba-la, Rhum-ba-la
Mercenairos y fascistas
Rhum-ba-la, Rhum-ba-la, Rhum-ba-la ...

Is that the same song Ian Campbell recorded?? If so, it's very different from Christy Moore's