can't setup locale
 

I used the command "echo "Setting locale" /usr/bin/localedef -i el_GR -f ISO-8859-7 el_GR" to setup Greek fonts. Where i found the the directions it also said
"Further you need to alter either your /etc/profile (for a machine wide setting) or create following lines in the corresponding ./profile. For /etc/profile find the line "export LC_ALL=POSIX" and alter (or create)

export LC_ALL=el_GR
export LANG=el"
However, i didn't find LC_ALL=POSIX. Anyway, i decided to reboot the PC. I opened a couple of Greek web pages, but the problem still remained, although the encoding was set to "ISO-8859-7 Greek".
I want to install Greek fonts and i found a lot of sights, which advise me to edit the "/etc/profile.d/lang.csh" file and use the "locale" and "localedef" commands, but nothing really works, or after rebooting i end up changing the system locale with unreadable characters.

What can i do? Please help. I use Slackware 10 and Gnome.