Translate Upgrades

I'm making a new payment option for the upgrades plugin (iDeal via Mollie.nl) and since that is for the Netherlands I want to translate the upgrades plugin to Dutch.
To be honest: I have no idea how to start. I do know how to translate a plugin when there's a .po file, but I have no idea how you make one of those things from scratch..

Could anyone point me in the right direction?