Hi there,
I have to say, my immediate thoughts after reading this is that you should go for the geography a-level. It is easier to excel in a subject that you love, rather than thinking about what the subjects might look like in combination, consider what it is you will gain both in terms of subject knowledge and enjoyability in the subject. Both German and history will still offer you a chance to be analytical and work on essay skills.
It also seems that you have your heart set on studying German or history, so maybe picking the subject that you honestly enjoy more would be the best choice.
Follow your gut instinct!