While upgrading an old gentoo box I encountered this error:

xgettext: error while loading shared libraries: libexpat.so.0: cannot open shared object file: No such file or directory

I tried fixing it with revdep-rebuild tool but it failed too. Through some research I found this is a common error consequence of a broken update process (nothing is perfect in this life) due to a circular dependency.

But you don't have to worry, there is a simple way to fix this:

kp ~ # emerge --unmerge --quiet expat gettext
kp ~ # emerge --quiet expat gettext

After this your emerge processes will run smoothly again.

-=kp=-