It's possible for a location or nation to recognize / use more than one currency at a time.
- There may be a Grain-based Local Currency and a National Currency that bears the King's Imprimatur. The former is stronger around harvest time, the other retains it's value year-round.
- A particular social or religious group might deal only with a certain specific currency, such as donations at a temple having to be in coinage bearing only religious iconography, no secular imagery or foreign gods.
- A company town might pay it's workers in Company Scrip that's valueless outside of the local community.
- Settlements in a War Zone, Neutral Zone or Demilitarized Zone may accept money from both countries, especially if the war could easily go either way.
- A small country with an unstable economy might officially only recognize it's own money - at the same time, most merchants are happier accepting payment in the more stable currency of a neighboring state.
- Or, like modern China, you could have a country that has two currencies - one that's only usable by locals / citizens, and another that's a form of Foreign Exchange Certificates, and the law only allows the later to leave the country or be owned by foreigners. Such a nation might go so far as to base the local currency on the Gold Standard, but use only the King's Imprimatur or other dubious "guarantee" of value. (Not saying China does, by the way, I know nothing about it and Wikipedia was pretty vague)
- After the Fall of Rome (or the equivalent), there may be a lot of old coins left in circulation. They may have lost a chunk of their value, but they are still worth the metal they were cast from. Or, in the midst of a Dark Age, if the ability to mint new coins (or refine ore) is limited now, the old coins may be more highly praised than the official currency.
- Twenty Minutes Into The Future, impoverished cities might see a rebirth of barter, or supplemental alternative currencies. The masses of unemployed workers have plenty of time and energy, but not much official money. Things that can be built locally, and traded for services or invested in the future, may be one way to pull themselves out of that rut. The Urban Prairie turns into community gardens, and the poor are sustained on local food and recycled clothing.
Game and Story Use
- A touch of this can provide flavor, and a way to make treasure hauls a little more interesting.
- Fiddling with Exchange Rates, Money Changers, and the like can be used to make treasure hauls more complicated, or to give the mental and socially based PCs one more way to contribute to the group. Careful not to overdo it, however, as heroism and adventuring probably makes for better games then complicated economics did.
- Very abstracted fluctuating currency values could make for an interesting setting, however. If the PCs buying power varies from session to session or city to city, they'll have to strike while the iron is hot, and hoard when it's not. If there's something the PCs can do to impact or take advantage of this, it could be a fun little minigame.
- And of course, there's plenty of adventures to be had trying to offload a chest of banknotes ahead of the news that the bank collapsed, or influencing a kingdom's fiscal policy to help out an investing friend on the borders. Or trying to stop someone else from doing the same.
- Some ancient cultures were fairly promsicuous when it came to currency and accepted pretty much any specii by its metal weight - even to the extent of hacksilver, where chunky silver jewelry served as currency with the wearer cutting pieces off to trade with. This tended to break down where adulteration of coinage became widespread and lead more or less directly to royal currencies where the mark of the mint was meant to attest to purity and provide a common reckoning for mass.
- Still, an adventure town or a city serving as a hub of trade could well accept any currency, ancient or modern by its bullion value, possibly at a discount for coins known to be frequently impure, with the merchants regarding a set of coin scales as standard kit.