Here in Switzerland it's even worse because it depends on where in Switzerland you're formatting the number (French parts have different rules from German parts) and whether you're formatting a number as a plain number or a monetary value.

if it's money, you use the . as the decimal separator everywhere. if it's just a number, in the French parts, it's , in the German parts the .

The thousands separator is ' everywhere

surely this must routinely cause horrific mistakes in things like bank transactions?

Norway as well