The gnome-keyboard-applet only permits me to set four language settings for the
keyboard.  The "Add" button is there until I've set four, after that it is
blanked out.

This behaviour is surprising and I think unhelpful.  I don't think it's too
hard to imagine situations where you'd want to have access to a half-dozen
or even more languages. Someone dealing in Middle Eastern/Mediterranean
affairs could easily want French, Arabic, Hebrew and English.  If they're
configuring for visitors they might want both UK and US English. Throw in a
Russian observer, and that's already six layouts needed.

The problem seems to be new in 2.10.  I'm pretty sure I could set more than 4
languages previously.

Apart from that the applet is working well.  Bugs #314792, #315537 and
#315717 don't affect me.

Drew

Bug #520625 looks like a duplicate of this one.

https://bugs.freedesktop.org/show_bug.cgi?id=19501

As a an easy workaround, which works at least for my needs:
download the kdebase-bin 3.5.9 deb of Debian Lenny, unpack (not
install), copy libkdeinit_kxkb.so v3 from bin/ directory to lib/, where
the kxkb v3 is. Then start kxkb from that directory. Braver people can
do more, like setting aliases to kxkb or even make a clean .deb.