With a browser, how do I know which decimal separator does the operating system use?

Question

I\'m developing a web application.

I need to display some decimal data correctly so that it can be copied and pasted into a certain GUI application that

Answer 1

I can guess the decimal separator from Accept-Language and the guess will be correct in 95% cases, but sometimes it fails.

This is IMO the best course of action. In order to handle the failures, add a link to set it manually next to the display area.