Comment by nephihaha

Germanic and Celtic languages have been in contact for at least two thousand years. Probably longer. There are Celtic loanwords in English which predate the Anglo-Saxon invasions. After the invasion, English took centuries to expand into areas which spoke P Celtic, and it seems to have profound influences on its verbal structure. Another wave of Celtic loanwords entered English via French.

As for modern English, there are numerous Celtic loanwords and calques in American, Canadian and Australian slang and dialect.