PayPal Portlet: call PP page in a specific language?

Using the PayPal module/portlet for eFire, do you know how to call the PayPal page with a specific language?
I know there is a URL parameter (add "&LC=ru" for example) offered by PayPal for this very reason, but I haven't found any way of setting up the eFire module accordingly.

I am using the module in version 1.5.5. (along with Oxid CE 4.2).

Thanks for any idea or suggestion!