Hmm I think you miss the point. In some programming environments (like C# and Java) .toUpper() is always incorrect in code unless you are displaying the resulting string in a UI, as it uses the "current locale", which is whatever the user has selected for the machine. When e.g. comparing strings case-insensitively, you should always explicitly specify the locale where the conversion should happen instead of relying on an external configuration variable.

JavaScript actually seems to be the smart one here - its default .toUpperCase() uses the "locale-insensitive case mappings in the Unicode Character Database".