Author: Simey Lameze
MDL-52490 mod_assign: fix lang strings to make it consistent
http://git.moodle.org/gw?p=moodle.git;a=commit;h=48da3eef6e22b84a722783c287b102bac4b41b5c
http://github.com/moodle/moodle/commit/48da3eef6e22b84a722783c287b102bac4b41b5c
+ 3.1 en [batchoperationconfirmdownloadselected,mod_assign]
+ 3.1 en [downloadselectedsubmissions,mod_assign]