There's actually no such language as "Celtic". Celtic refers to a group of dozens of languages, six of which are spoken today:
Pagani and Paganus meaning country dweller
Halloween started in Irland as a pagan holiday ,so it is celtic.
What I think the religion of the Celtic cross came from is probably the Pagan Druidic religion.
Halloween is a combination of pagan holidays, Sambain and Pomono.
It was the last night of the year in the old Celtic calender, a night for witches, known a Old Year's Night and was a Pagan holiday
GRAET ??
Yes, Wicca does exist. Wicca is a pagan revivalist religion that incorporates many ancient Celtic traditions with other pagan pantheons.
Brigid never "took over" any pagan cult. She was originally worshipped as goddess in the Celtic nation.
pagan
Celtaidd = Celtic
The Pagan worships idols. A Druid is a Pagan.
There are six distinct Celtic languages.
Halloween - is a Pagan festival - with its roots in Celtic history - nothing to do with ancient Greece.