There are two examples of this bug:
1) a posting to the forum: by Rob Rashotte - Tuesday, January 27, 2009, 12:47 AM
I (Rob Rashotte) have several language packs installed on my moodle site and it appears that if someone selects a language that uses a comma for a decimal place holder that the amount of the transaction is misinterpreted by authorize.net.

For example I have a course that costs $500 US.

If someone is using the default language settings then $500.00 is displaced as the price of the course and is interpreted by auth.net as $500.00

If Someone has the DE language pack selected (for example), the price is displaced as $500,00 but authorize.net is interpreting this as $500,00.00 or $50 Thousand dollars.

2) and my installation of Moodle (via MoodleRooms), have experienced the same issue.

We added a second course to our MoodleRooms site on Friday May 27, 2011. The new course is a 100% duplicate of the first course, except the course content has been translated into Spanish.

So, as part of the configuration of the new course, we configured the Spanish course content to "Force" the users to use Spanish language pack. After configuring this everything seemed to work fine, EXCEPT, the price of the course changes from $99.00 to $9,900.00; so when students try to register for the class, their credit cards are being declined because of this higher price.

The attached screen shot shows something we noticed when the Spanish Language pack is forced; the price of the course is DISPLAYED with a comma instead of a period after the "99".