For example, Daily format in calendar,
Friday, 1 February 2008 (English)
2008? 02? 1?(???) (Japanese): by modified function userdate()
2008?? 02? 1??(???) (Japanese): by original function userdate()

$format is multibyte characters(UTF-8) in japanese-lang-file.
But return value of strftime('%A') on japanese windows version PHP contains non-UTF-8 characters.

Therefore $format must be converted to $localewincharset at first in japanese environment. I think that there are no bat influences by converting $format to $localewincharset in other language.