A recent thread about 'debdelta' raised a question about
whether 'debdelta-upgrade' sources from apt's package cache
or one's running Debian system:

    secipolla                Posted: Jul 24, 10, 8:28
    apt-get clean is fine
http://techpatterns.com/forums/about1590-10.html

...according to Secipolla there, 'debdelta-upgrade' didn't use /var/cache/apt/archives.
it sourced from the running system.  I recently read some 'debdelta'
README files, but don't recall the question being addressed.  (But maybe I
missed something.)

For 'localepurge' users, the cached package is more complete than the
running system.  Is it feasible for 'debdelta-upgrade' to do something
like:

    1) check local system.  Has package been localepurge'd?
	a) yes: check apt's package cache then.  If currently installed .deb
	        file version is still cached, fetch missing locale files from that.
	b) no:  complain as before.


(BTW, I discovered 'debdelta' yesterday, and love it!  I still like
'localepurge', but I uninstalled it to make 'debdelta' run better --
I've more HD space & less spare bandwidth.  It'd be nice if both
programs cooperated better.)

Hope this helps...