All my knowledge about UnionPay is about RMB UnionPay cards.

The RMB UnionPay system is something like a closed system that everything charged is converted to RMB using UnionPay's own rate. It doesn't charge extra fees, but the rate includes the pay for the work (artificial but somewhat competitive rate).

I understand UnionPay is invading the rest of the world (like every other Chinese forces), but I don't have any idea how it's gonna build a multi-currency based system out of the current mostly RMB based system.