In the US, it's very common to add a comma for numbers of more than 3 digits (ex: 1,000 for one thousand ; 1,000,000 for one million ; etc.).
In France though, we don't use this at all and commas are used for decimal numbers only (ex: 2,46).
Do you know which countries are following the US rule, and which countries are not? Where can I find resources on this?