Microsoft Excel is the worst offender here. When you're on a locale with , as a decimal point it's not able to read CSVs with . as a decimal point. It uses ; instead of , as a field separator.

Delegating parsing user input is a good idea, but sometimes the input methods you can rely on just don't cut it.

By the way: The international way to express a decimal separator is a (thin non-breaking) space. There's no misunderstanding possible.