So I tried the french SNCF app and the booking was done in a couple of minutes, all tickets conveniently in the app - expect for the German leg of the travel. SNCF sent me a Deutsche Bahn paper ticket via snail mail.
(*) Tried for about a week, on different computers, my mobile, from another account. Sent a complaint, received an email answer that said they could not help me, but I could send my email to another address - except the other address was the very address I sent my complaint in the first place. Went to Deutsche Bahn office eventually, train I wanted was supposedly booked out, which I know wasn't true because booked it later via SNCF. They reluctantly tried to find me an alternative, but apparently they had to go through all the combinations manually. It took forever and wasn't successful either.