Author: David Mudrák
MDL-66500 lang: Add the unoconvwarning string back
It has been deprecated and removed by mistake.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=b49bf4299c257a6211de883f0925c87e3c7ca714
http://github.com/moodle/moodle/commit/b49bf4299c257a6211de883f0925c87e3c7ca714
+ 3.8 en [unoconvwarning,core_admin]