well....gosh, I've done this

I should know. I even put my Gnome to show everything in one language, but use too some characters which didn't at first be there by doing some stuff with locales..
actually I don't, at least at this very moment, know/remember any way other than changing locales..LC_ALL, for example might do it? in terminal/shell, type
locale
to see your _current_ locale settings. I'm not completely sure, as I haven't dealt with these for a while, but you could try doing (in shell/terminal)
set LC_ALL LOCALENAME
where LOCALENAME is one of the locales in locales-directory (I'm not sure if it's the same on Slackware, but in Gentoo they're in /usr/share/i18n/locales/ so check that out - if you find lots of xx_XX@yy and xx:_XX -type files, then find your own

like
set LC_ALL de_DE@euro
would use de_DE@euro -locale. but don't shoot me if it won't work
EDIT: I think, if you happen to screw up, you can recover with "unset" command in shell? I'd suppose so. the plain "set" command shows your current settings, or those that have been set (so LC_ALL won't necessarily be there yet)