I re-added this game to my main-account which was banned in the lasts wave and I can choose english (us), english (enGB), german, french etc... so its no German only, but ofcourse they are going to advertise it on German.
Diablo 3 als Download online kaufen - PC & MAC - Gamesload
Go there, click top right "zum Kauf"
Choose the 2nd option:
Ich habe noch kein Kundenkonto / Den Kauf ohne Registrierung fortsetzen bzw. sp?ter registrieren.
Enter your e-Mail there and click on 'Weiter'
Choose how to pay.
I guess you can only use
"Click and Buy"
choose it and click on "Kaufen" at the bottom. Depending where you are from, you can choose how to withdraw the money. Credit Card, debit card, bank transfer etc...