Author: David Mudrák
MDL-47883 admin: Fix missing string in the plugin validation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=fb1f2b9b2712bddd47e198a1371c0e7962db8249
http://github.com/moodle/moodle/commit/fb1f2b9b2712bddd47e198a1371c0e7962db8249
+ 2.8 en [validationmsg_foundlangfile,tool_installaddon]