http://www.php.net/manual/en/ref.gettext.php
While looking up something else in the PHP manual, I ran across the page for gettext. After a quick look, it seems like it may be superior to get_string and related moodle code.
It won't have the opportunity to investigate PHPs gettext in the near future, so I thought I'd mention it here, in case someone else has some time they can devote to testing it out.
I looked at it before implementing my method, but rejected it because it requires a PHP module that is not compiled by default (and thus is not available on most web hosts).