I have found questions about this subject since 2016.
I m writing this on June 2, 2018, do you have an estimate when this option will be available?
Please, let me know.
At this time, there is no update to provide and currently setting the currency is a part of the Stripe integration and your site can only be set to one currency. It is something we are actively looking into though!
It is a turning point for using Thinkific for me too, as I want to create courses for the european audience. I am german...