See MDL-9361 for more info about this
Ability to edit language in third party modules and plugins w/o copying the language files
blocks/search/lang files should be moved in lang folder
Problem with lang file names taht are used more than one time.
In fact, because it''s in core it should be
That was student code that slipped through the review. Core lang files should never be in the module space.
Verified in Moodle 1.8 and 1.9