dot versus comma for radix separator

Factual Questions
1

Is the convention of using a dot as radix separator and comma as digit group separator a convention of English (language) in general, or is it a national convention that happens to correlate very closely to English?

I often see people writing in English but using “Continental” conventions (comma as radix, dot as digit group separator). My gut tells me that this is simply incorrect: a failure to follow the conventions of the language. But I don’t know this for a fact, and couldn’t cite a source.

Please fight my ignorance. Thanks!

2

I suspect the 123.456,78 convention is more European, while 123,456.78 is more-or-less strictly American. But I think Mexico uses the same convention that we use in the United States. I don’t know about South American countries, or whether Brazil follows the same rules as other South American countries.

I used to work at a small company that wrote a cash register application program. We had some customers in Mexico. I was in charge of (among other stuff) the code that printed the receipts and many of the end-of-day reports. I made it use the 123.456,78 rule, but our Mexican customers asked us to change it to the 123,456.78 rule.

Here’s a more general question worthy of discussion (and I’ll be surprised if there aren’t already threads on it – anybody have a link to contribute?) – Just how many little conventions and practices do we Merkins do bass-ackwards from everybody else in the world?

Examples:
[ul][li] In America, we flip light switches down for off, up for on.[/li][li] Our carousels go counter-clockwise (seen from above). ETA: So the horses have their show side (the side more extensively painted and decorated) on the right.[/li] In bathroom or kitchen sinks with separate hot and cold water knobs, the hot water knob is on the left, and the cold water is on the right.[/ul]

3

Actually, in much of Europe the decimal separator is , only since the advent of computers: previously, it was ’ (in many languages called a “high comma”, which is what I guess led to the mistake when it got coded into computers). I’ve had customers in half a dozen Latin American countries and decimal separator varied from location to location; sometimes, which decimal separator got used boiled down to “personal preference”.
Spanish used to request subscripts for million ([sub]1[/sub]), billion ([sub]2[/sub]), etc., but again computers have pretty much done away with that.

4

Let me look that up on wikipedia for you:

The article also shows a handy map: Decimal separator - Wikipedia

5

OK, so all English-speaking countries use the convention, and countries where both English and French are standard, the convention for English is the same as elsewhere.

So, in an international context, it’s sensible to use the English-speaking-country convention when writing in English. But not a hard and fast rule.

Thanks