document code to make mksh set ±U match the user locale from the environment

cf. http://thread.gmane.org/gmane.linux.debian.devel.bugs.general/1246729/focus=606

mksh.1

@@ -1,4 +1,4 @@
-.\" $MirOS: src/bin/mksh/mksh.1,v 1.358 2015/04/11 22:09:49 tg Exp $
+.\" $MirOS: src/bin/mksh/mksh.1,v 1.359 2015/04/11 22:35:10 tg Exp $
 .\" $OpenBSD: ksh.1,v 1.159 2015/03/25 12:10:52 jca Exp $
 .\"-
 .\" Copyright © 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
@@ -6481,6 +6481,24 @@ will cause the shell (either
 or
 .Nm lksh )
 to behave more like the standard expects.
+.Pp
+For the purpose of
+.Tn POSIX ,
+.Nm mksh
+supports only the
+.Dq C
+locale.
+For users of UTF-8 locales, the following sh code makes the shell
+match the locale:
+.Bd -literal -offset indent
+case ${KSH_VERSION:\-} in
+*MIRBSD\ KSH*\*(Ba*LEGACY\ KSH*)
+	case ${LC_ALL:\-${LC_CTYPE:\-${LANG:\-}}} in
+	*[Uu][Tt][Ff]8*\*(Ba*[Uu][Tt][Ff]\-8*) set \-U ;;
+	*) set +U ;;
+	esac ;;
+esac
+.Ed
 .Sh BUGS
 Suspending (using \*(haZ) pipelines like the one below will only suspend
 the currently running part of the pipeline; in this example,