their weren't many 'real' german tribes at the time of caesar. that is, from a linguistic point of view. the rhine wasn't a linguistic/cultural border till the time of august. its hard to make a distinction in 'civilisations' when no written evidence (from themselves) is present. archeologically speaking we find the same items east/west of the rhine.

archeologist tend to make a difference between celtic speaking 'germans' at the time of caesar and german speaking 'germans' at the time of caesar. a migration took place between these 2 rulers. caesar spoke of germans only to justify he didn't march east of the rhine (he was there to conquer gaul, since they kicked his ass east of the rhine they weren't germans , smart dude he was )