This is a really simple question, but the answer is stumping me: How do you format another country's currency correctly?
Specifically, this answer, quoting from Wikipedia, has a great survey of how various countries format large numbers in their system:
In English Canada, Ireland, Israel, Japan, Korea (both), Malaysia, New Zealand, Singapore, Taiwan, Thailand, the Philippines, the United Kingdom, and the United States: 1,234,567.89 or 1,234,567·89; the latter is generally found only in older, and especially handwritten, documents. Australia used this style up until the 1970s; now it uses the SI style
In Mexico: 1'234,567.89; for million separator an apostrophe is used.
In India, due to a numeral system using lakhs (lacs) (1,00,000 equal to 100 000) and crores (1,00,00,000 equal to 10 000 000), comma is used at levels of thousand, lakh and crore, for example, 10 million (1 crore) would be written as 1,00,00,000.
Assuming I conducted a transaction for $4,999,999.99 in the US system of formatting, using USD for the currency. If this transaction is later viewed in a version of my site localized for Mexico, do I display it as $4'999,999.99 to match their number formatting? $4,999,999.99 to match the original currency? In India, would it be $49,99,999.99?
Related: Would the currency symbol follow the country's conventions for placement, or would it always be in front (as is the standard for USD)? What about negative values?