This one took me a while to figure out, which is reason enough to post it here.

First of all, you’ll need aspell-he, as pidgin uses gtkspell (which, in turn, uses aspell) rather than enchant (which supports hspell). There is a patch for gtkspell which gets it to use enchant, but I don’t know of a simple way to get it to work in my distribution of choice, Ubuntu.

Now you need a neat little plugin from the Guifications plugin pack, called SwitchSpell. Unfortunately, it’s in version 2.3.0 of the pack, whereas the current Ubuntu version is 2.0.0. It’s not complicated to install this from source though: I’ve detailed the precise installation procedure below; the confusing thing is that if you forget to install libgtkspell-dev or libaspell-dev, SwitchSpell will not be built, but the configure script tells you that it will.

sudo apt-get install build-essential gettext libgtkspell-dev libaspell-dev pidgin-dev
tar jxvf purple-plugin_pack-2.3.0.tar.bz2
cd purple-plugin_pack-2.3.0
./configure --with-plugins=switchspell
sudo make install

At this point, the Switch Spell plugin should show up in your Pidgin preferences. When you activate it, you should get a menu at the top of each conversation for choosing the dictionary in use. Enjoy!