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.
It is a turning point for using Thinkific for me too, as I want to create courses for the european audience. I am german...
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!