Jamie here from Shopify. Our POS solution is currently available worldwide! The caveat for international merchants is that we do not have the means to ship hardware internationally at this time, and our Payment Gateway Shopify Payments is not currently available for POS outside of Canada and the US. That being said, there are work aronds for both. Check out this link for a list of third party vendors that sell Shopify supported Hardware for countries out of CAN/US. You can also reference this list if you need to go through a different source. As far as actually taking payments, you can use any card reader payment solution(s) you would like. In this case you are marking these orders as paid using an External Debit or Credit terminal. This Shopify Doc goes into more detail.
I hope that helps! Cheers,
Jamie | Support@shopify.com