Localization and internationalization of an app or site it’s a challenge that’s not specially hard on the technical side, but that it can ceirtanly become difficult for social and behavioral aspects, such as our own etnocentrism, lack of standardized standards, or even standards that conflict with actual use or user expectations.
The development team at Etsy identified three attributes that affected currency formatting: the currency, user location and user language. Their post on How Etsy Formats Currency shows how to correctly format currency and some of the practical decisions that are involved in the process.