This is an old thread but wanted to share my experience.

Here are the rules for complicated bookings that involve different region credit cards and paying for a miles ticket:
- the credit card you are using must be in the name of the AAdvantage accountholder
- the reservation on hold must be quoted to you in the currency of the credit card you intend to pay with. If you need to pay with a German credit card, you need to find a way to log on to AA.com Germany and hold the reservation and get it to quote you in not only Euros - but based in Germany. This is easier said than done because if you log in with your US based account on German AA.com, it will still book and quote you in US dollars. So you can either login and book/hold with a German friend's AA.com account or just create a dummy AA account, German based solely to accomplish this task.
- I am aware that at the checkout page there is an option "to change the region of payment" but sorry folks, it doesn't work, that's why I created this workaround.

The reason this is complicated is:
- AA website is inflexible - the held reservation must be established and price quoted in the region where you made it. AA Germany, AA Canada
- but in order to hold a ressie in AA Canada, you have to have a AAdvantage account based in AA Canada (my AAdvantage is USA) So in order to circumvent this - you create a dummy account as above, or I guess you could change your account region to Canada - but that sounds more complicated and problematic.
- once a held reservation is booked, the ressie is tagged ie Germany, Euros; Canada, CDollar, etc
- so then to pay for it at the payment page, you are locked into Germany or Canada etc and there is no way to change this (and the option AA.com gives you doesn't work)

I understand that explaining this is kinda muddy so if any one needs advice, please message me.