Locale + encoding combinations

I'm working on some code for pgInstaller that will check the locale and
encoding selected by the user are a valid combination.

The changes recently added to initdb (which highlighted the UTF-8 issue
on Windows that Tom posted about) appear to only allow the default
encoding for the locale to be selected. For example, for me that would be:

"English_United Kingdom.1252"

However, setlocale() will also accept other valid combinations on
Windows, which initdb will not, for example:

"English_United Kingdom.28591" (Latin1)

Is there any reason not to accept other combinations that setlocale() is
happy with?

Regards, Dave