I'm using the latest version of pidgin-plugin-pack in lenny, and it seems this bug is open for 4 months now, and there's still no SwitchSpell plugin inside pidgin-plugin-pack. I'm using amd64, and I don't even see the switchspell.so plugin in the .deb.
I'd really love to use that plugin - if there's a way I can help, I'll gladly do it.