Almost all of them, judging by software I've been dealing with on both Windows and Linux systems, as well as the web. Even the big companies full of smart people get it wrong - as evidenced by Excel, and the problems like those described in TFA.

The problem doesn't even have a correct solution, because the locale settings in the OS and the browser aren't often set by end users (a regular person probably doesn't even know that they exist) and the defaults depend on many random factors (like which store you bought your computer with preinstalled Windows from).