Hi,
I remember when the "filterall" functionality was introduced long time ago. It caused hundreds (say, X) of small (trivial) modifications in order to allow every little string in Moodle to support the multilang filter.
And then, we arrived to 2 strings:
course->fullname
course_category->name
that themselves needed 4X modifications in code (trivial too) to have multilang support working on them.
So, due to time for release we left them out. Since then, well, time availability has been a problem, release after release and, sincerely, it hasn't been in my (our) "top list" since then.
There is one docs page to document all this:
http://docs.moodle.org/en/Development:Filterall_support
And perhaps it would be interesting to add some report to the bug tracker:
http://tracker.moodle.org (if it doesn't exist) and to vote and comment about it in forums in order to get/gain some priority.
It's shouldn't be difficult at all but will be a long task, slooooooow to apply and test everywhere (because of the number of places to modify in Moodle code).
Ciao
