The fiat currencies used in every country in the world today are irredeemable. There is no mechanism to return a currency to its issuer in exchange for a legally-mandated fixed sum of gold or anything else. Irredeemable currency is not a feature of a free market, but of government intervention (and not coincidentally, it is Plank #5 in Karl Marx’ Communist Manifesto). Irredeemable currency has flaws which lead to suboptimal outcomes, which lead to demands for more interventions. International free trade requires money which is free from government interference generally, and specifically not under the control of one government. That money was gold, historically, and will be gold again.