Having a look at what #Deutschlandticket purchase route is best if you're not resident in Germany (and indeed don't even speak German)
Both DB and BVG (Berlin) oblige you to use a direct debit from a bank account to buy the ticket
The Deutschlandticket App established by a bunch of Verkehrsverbunde might work, medium term, but is only in German for now https://deutschlandticket.app/
So the best bet looks to be HVV (Hamburg) - in English, and can pay with a credit card https://www.hvv-deutschlandticket.de/en/faq/
@jon Yes, but getting that one right is not a given either, unfortunately.
@cweickhmann Right. It ought to work via SEPA. But cancelling that could then be more of a pain. And generally: more payment options are better IMHO.