Don’t go bringing that crackpot Edward Gettier into this. Caesar would know the Germans (those who hail from Germania) as a disorganized, unorganized group of tribes with a common heritage. That’s a justified true belief, or at least as justified and true as one could expect of him. His beliefs would not cover a unified German nation, at which point there can’t be a belief part of a JTB.

The Holy Roman Empire was not a contemporary of Julius Caesar nor was it united. If your subdivisions are fighting wars with each other then I don’t consider that a proper “country”.