Brythonic Celtic languages: Welsh, Breton, Cornish (dead)
Goidelic Celtic/Gaelic languages: Irish Gaelic, Scottish Gaelic, Manx
The Brythonic language is thought to be simlair to the Gaulish Celtic spoken in France, Belgium, etc., whereas the Goidelic Celtic language is thought to have been simlair to the Ibero-Celtic spoken on the Iberian penisula.
Celtic and Germanic are both groups within the Indo-European family of languages and are also both western Indo-European “centum” language groups (though others group Celtic with Italic and Germanic with Balto-Slavic, which is a member of the eastern “satem” group).
The druids in Ireland would of spoken Goidleic and the driuds in Great Britain would of spoken Brythonic.