I'm not at the Mac right now but 2 things to check:

System prefs, international I think: check only British English or whichever is activated, look for button called Edit List.

Large font libraries, if you installed lots that you don't use remove them with Font Book. Don't mess with the default OSX installed though.

Leopard generally runs slower on all PPC machines that I've tried including faster G5s than yours. Some of it I feel is software related so there's only so much you can do, as you have done with RAM.