We are using QuickPay payment plugin
quickpay.net/integrations/hikashop
So you believe it's to blame?
EDIT: Looking at the payment plugin, it seems the correct language parameter is sent when looking at the notify URL:
$notify_url = HIKASHOP_LIVE.'index.php?option=com_hikashop&ctrl=checkout&task=notify¬if_payment='.$this->name.'&tmpl=component&lang='.$this->locale . $this->url_itemid;
BUT, when looking at the callback from the payment provider, I see this in the URL:
index.php?option=com_hikashop&ctrl=checkout&task=notify¬if_payment=quickpay&tmpl=component&lang=da&Itemid=751
Is lang=da correct? In the database, order_lang is da-DK