As a plugin or theme developer I love to have my po/mo files living inside my packages language directory, so I can add it to my next plugin release.
As a blog admin, who simply wants to localize a WP installation or maybe adapt some wording to his individual requirements, I would rather prefer my translations to be stored in
WP_LANGUAGE_DIR, so they don't get zapped by a plugin update.
An option like "save in package dir" vs. "save in WordPress language dir" would be helpful.
Thanks, still a great work!