Comment by charcircuit a day ago
Everyone who has used Java has hit this before. Java really should force people to always specify the locale and get rid of the versions of the functions without locale parameters. There is so much hidden broken code out there.
The invariant locale can't parse the numbers I enter (my locale uses comma as a decimal separator). More than a few applications will reject perfectly valid numbers. Intel's driver control panel was even so fucked up that I needed to change my locale to make it parse its own UI layout files.
Defaulting to ROOT makes a lot of sense for internal constants, like in the example in this article, but defaulting to ROOT for everything just exposes the problems that caused Sun to use the user locale by default in the first place.
That only helps if devs specify an invariant locale (ROOT for Java) where needed. In practice, I think you'll see devs blindly using using the user's current locale like it silently does today.