I like the support for custom currencies, as that is an edge case that often pops up.
On the other hand, be careful about tying the symbol to the currency, as symbols are locale specific. For example, the symbol for USD is $ in eu-US but US$ in en-CA and en-AU (Canada and Australia), and then $US in French locales.
https://cldr.unicode.org/ is the magical dataset behind most good implementations that deal with currency display. Updated twice a year, available in JSON, providing currency symbols and formatting rules for all locales, as well as country => currency mappings and other useful information.
On the other hand, be careful about tying the symbol to the currency, as symbols are locale specific. For example, the symbol for USD is $ in eu-US but US$ in en-CA and en-AU (Canada and Australia), and then $US in French locales.
https://cldr.unicode.org/ is the magical dataset behind most good implementations that deal with currency display. Updated twice a year, available in JSON, providing currency symbols and formatting rules for all locales, as well as country => currency mappings and other useful information.
Disclaimer: I maintain a Go solution in this problem space: https://github.com/bojanz/currency