The AdminShop mod already supports changing the currency symbol by modifying the translated string for gui.money_message:

However, the result only makes sense for currencies and languages where the currency symbol should precede the number, which is a subset of all currencies and languages.
In some European languages, the euro symbol (€) comes after the number with an intervening space: "123 €" instead of "€123."
Would it be possible to refactor the way monetary amounts are formatted to support this?

Another example: Suppose I want to translate the balance display in the top left into Japanese and use Japanese yen instead of dollars. If I do so as far as I can, I will end with the following, which is incorrect:

Balance: 円13500

I expect the following:

残高：13500円

(the word "Balance" not being translated is a separate issue.)

Added