^{This is based on a StackOverflow question.}

Package golang.org/x/text/number allows locale-specific formatting of numbers à-la fmt. Unfortunately, unlike fmt, this package doesn't have an interface to let types other than the built-in numeric types tell the package how to format them. Or rather, the interface is there, but it's in an internal package, so the users can't really implement it.

This wouldn't be bad if math/big types or types whose String() method produces numbers were supported, but as of now that is still a TODO.