Add new on-wiki report for newly added MediaWiki core languages

<https://translatewiki.net/wiki/Thread:Support/Announcing_when_languages_pass_the_translation_threshold_to_be_exported_to_MediaWiki>

Change-Id: Ifde61245cc31fc11f5edfbd4c2581e4eddade29b
Merge "Add new on-wiki report for newly added MediaWiki core languages"