Why does Bimetallism require international cooperation to have a chance at succeeding? I was reading the Britannica encylopedia's article about Bimetallism and under the arguments put forth against it, they cite that bimetallism doesn't work without international cooperation. Could anyone explain to me why this is? I can't seem to find a succinct answer to my question.
Quoting Wikipedia:

Bimetallism[a] is a monetary standard in which the value of the monetary unit is defined as equivalent to certain quantities of two metals, typically gold and silver, creating a fixed rate of exchange between them.[3]

Let's suppose that France says 1 ounce of silver is F1 (1 franc) and one ounce of gold is F80. And let's suppose that Germany says 1 ounce of silver is DM1 (1 Deutschmark) and one ounce of gold is DM79.
Anyone with an ounce of gold and a bit of common sense will go to France, convert it to francs (80 francs), convert it to silver (80 ounces), go to Germany, convert it to Deutschmarks (80 Deutschmarks) and convert it back to gold (1 ounce + 1 Deutschmark left over). Then they'll do it again. Over and over and over and over. Every time, they get an extra Deutschmark. Until France runs out of silver or Germany runs out of gold.
The only way this can be stopped, is if every country uses the exact same ratio - for example, if they all agree that 1 ounce gold = 80 ounces silver. That is international cooperation.