A very curious statement. Saxon is/was a German language, not at all a Celtic one. The Saxons (along with their Angle and Jute brethren) expanded at the expense of the Celts in the waning years of the Roman Empire in the West, at first on the continent, then raiding and eventually invading the Celtic refuge in the British Isles.
Whether or not Saxon is meant, you have the problem that all members of the Indoeuropean language family (Celtic, German, Latin, Slavic, Indo-Iranian, etc.) are more related to each other than any of them are to the Semitic languages (Hebrew, Aramaic, Ancient Egyptian, Assyrian, Akkadian, Arabic, etc.). You have to account for a transformation that jumps across the tree of language evolution from one pre-existing branch into another pre-existing branch in some way that makes historical sense.
And then you have that there were already Celts, as it looks to most people who have looked into the Celts. It's hard to completely become somebody who's already out there.