economics - Are the wizard coins in the Harry Potter books international?

The Galleons, Sickles, and Knuts are described as the currency of wizards. I don't remember seeing anything about any other currency used by wizards. Is there such currency? Are Galleons, Sickles, and Knuts universal, or do wizards outside of Britain/Commonwealth/English speaking world use different currency?

Answer

There is almost certainly some kind of different currencies, though there's not enough canon info to know if they are some rare outlier country's coin, or every country has it own coins. From Goblet of Fire, Chapter 7 - BAGMAN AND CROUCH

"You foreign?" said Mr. Roberts as Mr. Weasley returned with the correct notes. "Foreign?" repeated Mr. Weasley, puzzled.
"You're not the first one who's had trouble with money," said Mr. Roberts, scrutinizing Mr.
Weasley closely. "I had two try and pay me with great gold coins the size of hubcaps ten minutes ago."

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  Neither Galleons, Sickles, or Knuts are even remotely close to the size of hubcaps

  
  


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  On the other hand, Galleons aren't very much bigger than muggle money, so Mr Roberts wouldn't be calling them "great gold coins size of hubcaps" if they were simply Galleons.

  
  
  
  
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    British 2 pound coin is 1.12"

    
    
  
  
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    Wikia says Galleons are the size of American Silver Eagles, ~1.6" (mere 50% bigger). No cite, but seems about right given they were carried in kids' pockets.

    
    
  
  
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    hubcaps are at least 10x the size of a Galleon, 15x size of 2quid (Toyota RAV4's is 16")

    
    
  
  
  
  

Therefore we almost certainly can infer that they were something else (and I know of no Muggle currency of that size).

But there's no additional info on the topic I'm aware of in HP books, interviews or podcasts (however, there's a chance future post 4/2013 data on Pottermore would add some extra details).

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NOTE: in the interest of fairness, there exists a legitimate opinion (voiced on both on HP Wikia's talk page and in comments below) that Mr. Roberts was given typical Galleons and merely used "hyberbole" when he compared the slightly-larger Galleon coins to "hubcaps". I personally don't see it as a plausible interpretation (see above), but there's no unambiguous proof it's wrong.