Hello @BlueBottle!

Square can process most Internationally-issued cards with the Visa, Mastercard, Discover, AMEX, JCB, and Union pay logos. The processing fees are the same as accepting a US issued card, but your customer might have to pay a conversion fee to their bank. 

You can find this information in our Support Center Article Accepted Cards. 

If you still have questions please feel free to reach out!