Join Date: Aug 2015
Location: DXB
Programs: AA EXP, A3 *G, LH SEN, SK EBG, Marriott Titanium, Hyatt Globalist, Hilton Diamond, etc. etc....
Posts: 3,334
That would be possible, but the US card is much better than the German card. US points transfer 1:1 to travel partners, German points transfer 5:4 at best.
The only advantage with the German card would be local Amex offers, and you wouldn’t be able to use things like the Uber credit that the US card comes with.
You’ve already mentioned FX fees.
The German card has different transfer partners, like Qatar Airways and SAS.
You can get a German Visa/MasterCard like the Miles&More credit card, then use that to transfer money into your US bank account to pay off your US card. That way, you’d earn both US Membership Rewards points and Miles&More miles.