Hi,
The HikaShop team did not implement that plugin ; we do not have any developer documentation or test account.
It is the main reason why the Sofort plugin has been removed from HikaShop package and externalized.
github.com/HikaShop/hikashoppayment-sofort
If you have access to the developer documentation and have a test account ; you can see to modify the Sofort plugin to add your currency and then propose a "pull request" for your improvement patch.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.