wow really? thats so cool hahaha then i'd go with germanicae for sure
but if you like, he can be relegated to an ancilliary or something. And yea but from what I can see Germanicae is in russian lands sort of-ish and there are one or two allusions to them being russian so that was my reasoning, but you could have Barbarossa(the plain but I guess expected choice(thanks AOE2)), or Frederick the Great who was prussian and not from this timeline, but who's keeping track?
Hispannia could get El cid or that guy that went to America though his name escapes me, I think it's Cortez.
As you said Francia could get Charlemagne or charles martel
Shambala could get... Ghandi maybe? More as an amazing governor I guess that one is tough
Islamic peoples could have Saladin or like the baron of Ybellin to be polarizing though it wouldn't make too much sense to have B. of Ybellin cause he was a diehard zealot in real life not who Orlando plays
And well Satanae gets Lucifer
EDIT*** Shambala could get Attila or Genghis Khan