Tcl9: source files are interpreted as utf-8 by default

Folks,
is it possible in Tcl9 to get the old (8.x) behaviour back,
that tcl files are read with system encoding instead of
utf-8?
Is there e.g. an environment variable or a configure
switch to change this?
I found:
--with-encoding         encoding for configuration values (default: utf-8)
but, what is meant with "configuration values"?
I've the problem that almost all of my sources contain some
umlauts and are, for legacy reasons, in iso8859-1. If it's
not possible to get the old behavior back, I have to
edit every pkgIndex.tcl and every tclsh <script> call
before I'm able to migrate.
Thanks in advance
Uwe