Langdisplay: Multilanguage TOC improvements

This pull request it's only for https://github.com/marcbria/pkp-lib/commit/eb462df23f1307b818d06fb3af932564d18f1444
(changes in "classes/submission/Submission.inc.php")

BTW, I need the first two commits to let OJS work with mOJO... so how could I tell github to ignore former commits?

Yes, a link with a RTFM is deserved here... :-D