High German didn't exist yet, though. The High German sound shift hadn't happened yet. At that time all the West Germanic dialects would have been closer to wh

High German didn't exist yet, though. The High German sound shift hadn't happened yet. At that time all the West Germanic dialects would have been closer to what we call "Low" Germanic now; Dutch, Low Saxon, Frisian, etc. Harder consonants where German now has softer ones. And I imagine it was probably easier for them to muddle through mutually understanding each other back then. But yes, in addition to Gallo-Romance, he probably spoke something similar to Old Low Franconian, which eventually became Dutch.