There's actually no such language as "Celtic". Celtic refers to a group of dozens of languages, six of which are spoken today:
Celtic languages originate from the British Isles and France.
Celtic.
The first Indo-European language spoken on the British Isles was likely Common Brittonic, spoken by the Celtic Britons during the Iron Age and Roman period. Over time, this language evolved into various Brittonic languages such as Welsh, Cornish, and Breton.
Celtic is a language/ethnic group from the British Isles. Christian is a religion that is not tied to any specific ethnic group or language.
Celtic is not the same as British. The Celts lived in the British Isles, but also through much of what is now France and Germany.
Celtic peoples.
There are at least nine languages native to the British Isles, including:EnglishCornish (Kernowek)Welsh (Cymraeg)CumbricScotsScottish Gaelic (Gàidhlig)NornManx (Gaelge)Irish (Gaeilge)Most of these are Celtic, and the Celts brought that from afar. English derives from Saxon with Viking influences. Norn, is from Scandinavia. Nobody knows what native language was spoken in the British Isles pre-CelticThe languages of the British Isles are the various Celtic languages brought by various Celtic migrations, and what is called English which developed from what displaced the Celtic (largely Welsh) spoken in England before the Saxon and Viking invasions of the dark ages. Interestingly, Latin did not persist. So no languages spoken in the British Isles are native. No-one knows what was spoken before the Celtic migrations. Basque?
No, he was from the British Isles, so he was likely Celtic.
The Celts came from Europe (Including the British Isles).
Yes, if it was a Celtic Christian saint, of he is. Christianity came to the British isles in the Celtic Era and there were many Celtic Christian Martyrs, who are called as saints.
In England, before English became the dominant language, a combination of Old English and Latin were commonly spoken. Prior to that, various Celtic languages were spoken in the British Isles.
British Isles