UTF-8 is great, I mean, this is wonderful. The problem is, it’s not yet well supported, and most of the stuff I have is in Latin1 (aka ISO-8859-1), and not UTF-8. That’s why I would like all my apps to have Latin1 as a default.

I haven’t found a straightforward way to tell that to Fedora and/or KDE and/or Linux.
So I had to make a couple of modifications to some files…

First, tell GDM (this is the program that displays the login page, before opening your window manager) you don’t want UTF-8. In the /etc/gdm/locale.alias file, I’ve replaced

French                  fr_FR.UTF-8,fr_FR

by:

French                  fr_FR.ISO-8859-1,fr_FR

Second, tell all the others apps you want Latin1 as a default. This is controlled by the LANG environment variable. To know your current LANG value, type:

$ echo $LANG

A more complete command to get the same result is locale without any arguments.
My LANG is fr_FR.UTF-8. This is not what I want. So I modified the /etc/bashrc file (system-wide autoexecuted bash file), and added at the bottom:

export LANG="fr_FR.ISO-8859-1"

That’s it!
I had to logoff/logon to apply all the changes (due to gdm)
Edit years later: Well, I finally switched to a full UTF-8 system :)