from GS thread:
Have a way for the user to define custom currencies. One use for them would be "derivative assets", like air miles and the such.
[not-tagged:"suggestion" tagged:"feature" bulk edit command]
Another reference to it
(from [a428af30f3a8]) Added CurrencyProviderPlugin
This allows for custom currencies. It even allows for custom providers for
exchange rates. [#33 state:fixed]