There have been a few updates in Xorg regarding the multilingual keyboard support.
First, a new dead key has been added for Finish, dead_stroke. It appears that Cyrillic would find it useful as the available dead keys are too few to be reused in this case. The moral of the story is that if you want to add a dead_key, justify the necessity and it can be added.
Second, the Compose file nls/en_US.UTF-8/Compose.pre has been updated so that any Unicode keysyms have a value over 0x100000 (if keysym is Unicode keysym and had value < 0x100000, add 0x100000 to its current value). You will not see the change in the previous URL (which shows that CVS only); the updated Compose file is in git.
Thanks to Daniel Stone for going through these patches.
To get your daily fix on changes applied to Xorg, see the web-based interface to git.
Update (6Feb07): The new location of the compose file is http://gitweb.freedesktop.org/?p=xorg/lib/libX11.git;a=tree;f=nls