You'd have to buy a German Civ3. You might go be able to go through and edit everything, but it would be a long and tedious task. Much easier to spend the $10 on a German Civ3 and reinstall it.
As for being able to d/l the original graphics or files for a German Civ3, you won't get them here. We have a strict 'No Piracy' rule, and posting such files would violate that rule. Even if it technically isn't pircay.