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?
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."
Neither Galleons, Sickles, or Knuts are even remotely close to the size of hubcaps
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.
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).
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.
Definitely Hyperbole. Besides you realy want to base your opinion on somebody who is almost non stop confunded?
Wiki tels us that:
"Gringotts Wizarding Bank is the only bank of the wizarding world"
On the other hand wiki also tels us that:
"Currency in the wizarding Britain consists of three different coins. In decreasing order of value, they are: Galleon, Sickle and Knut."
So it never states what currency is used in other counties. Id like to believe that since Gringots is international it sets the currency meaning Galeons, Sicles and knuts.