The output of g_get_user_name is so ill defined that none of the callers
that I located via google use it right.  I would guess that no-one is.
There ought to be one or more wrappers that allow applications to use it
right.  There seem to be two classes of uses:

1. UTF-8 for display.  Here's one from Nautilus:

      return g_strdup_printf (_("%s's Home"), g_get_user_name ());

   A variant for this should validate for UTF-8 and convert/transscribe
   to UTF-8 for anything that isn't.

2. For filenames.  Here's one from Gimp 2.3.18:

      gchar *user_name = g_strdup (g_get_user_name ());
      ...
      subdir_name = g_strconcat (GIMPDIR ".", user_name, NULL);

   A variant for this should ensure that the encoding is right for filenames
   and that no invalid characters occur in the name.  Gimp tries to do that
   for Win32, but does not get it right.


(Also, the docs for g_get_user_name fail to mention that while the
encoding uses is undefined, it is an encoding that uses zero termination.)