We have got a Swish payment account with Nordea. We use Quickpay as "Technical Supplier". The site for payment got Danish laguage (we would like it to be in Swedish). According to Quickpay they get the laguage from the Virtuemart plugin. I can't find any laguage settings in the in Virtuemart. All our Joomla site is in Swedish.
We use Swish with Quickpay for CBSubs, and that works fine (in Swedish).