welcome or you're welcome.
Is 'cead mile failte' a response to someone saying thank you or is it welcoming someone (to a place)?
That's only when you welcome someone to a place. To say you're welcome you'd use tá fáilte romhat (which can also be used to welcome someone to a place) or go ndéanaí a mhaith duit. The latter is considered to be less influenced by English, though the former is used by native speakers in Connemara.
You could also use a phrase like ná habair é, 'Don't mention it'.
they are starting to teach their native language in schools again over in Scotland and Ireland because they feel they should stay in touch with their ancestry