Workaround
I can modify the Transaction History CSV file they provide to a koinly-readable format by renaming some columns:
  • Ausführung
    to
    Date
  • eingehender Betrag
    to
    Received Amount
  • eingehendes Asset
    to
    Received Currency
  • ausgehender Betrag
    to
    Sent Amount
  • ausgehendes Asset
    to
    Sent Currency
  • Transaktionsentgelt
    to
    Fee Amount
  • Entgeltwährung
    to
    Fee Currency
The other columns don't need to be renamed (they will be ignored)