In my head the barbarians wouldnt have had such regimented, standardised armies.

I think of the warlords elite troops concentrated in sections of the barbarian line, and while the rest of the army may be armed with similar weapons armour would vary from tribe to tribe. Breaking from the ranks as the armies engage would come individuals or small groups of frenzied warriors- call them berserkers, woad warriors or head hurlers.

I dont see them as formalised units- more young men bent on glory, taking massive risks and seeking recognition.

Im not maning that the armies wouldnt have tactical subtlety, more that the apearance of the army would reflect a multitude of tribes and families called together to fight.