will have a different first day of the week, if not a "full" Locale is used.
We use "language-only" Locales (e.g., de, en, fr, it), but the CLDR uses
the region to determine the first day of the week. I'm not sure *if* it
should be fixed, because it makes more sense to actually.
But it's kind of a breaking change, if we don't switch to full locales,
which will bring other problems with correct locale resolution.
It can be "fixed" by setting the locale provider lookup order of the
Maybe there should be a way to configure region fallbacks for Locales