Celtic would be better. Gaelic literally means coming from the Gaels, aka the Irish. Welsh and Cornish are Brythonic language speakers, not Goidelic/Gaelic, but they are all Celtic languages. The Angles, Saxons, Frisians and Jutes invaded Celtic Britain starting in the 400s.
Gaelic Isles
Celtic would be better. Gaelic literally means coming from the Gaels, aka the Irish. Welsh and Cornish are Brythonic language speakers, not Goidelic/Gaelic, but they are all Celtic languages. The Angles, Saxons, Frisians and Jutes invaded Celtic Britain starting in the 400s.