Author: David Mudrák
MDL-47883 admin: Fix missing string in the plugin validation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=c58c99db60ed854f4fb182cb637c2865316c3631
http://github.com/moodle/moodle/commit/c58c99db60ed854f4fb182cb637c2865316c3631
+ 2.6 en [validationmsg_foundlangfile,tool_installaddon]