As a complete layman with a curiosity-based interest, I'd have to guess it was (what is now called) Welsh, surely? Could it have been some lost continental Ger

As a complete layman with a curiosity-based interest, I'd have to guess it was (what is now called) Welsh, surely? Could it have been some lost continental Germanic/Celtic tribe? Seems less likely on balance. Maybe a big discovery still to come that will clear it up. A tomb somewhere under a housing estate in Glasgow or something.