In February 2016, KDE wikis have been upgraded to MediaWiki 1.26.2 and MLEB 2016.01.
Many issues have been fixed since 2012: mediawikiwiki:MediaWiki_Language_Extension_Bundle#Previous_releases
One of the new features is Special:PagePreparation + Special:PageMigration, which helps convert old non-Translate pages to Translate-powered translatable pages:mediawikiwiki:Help:Extension:Translate/Page_translation_administration#Migrating_to_page_translation
Issues 1-5 already on Nikerabbit's roadmap
[11:05] <annew> Nikerabbit: if I remove all <translate></translate> tags from a page, will it cause any problems? I want to remove that page from the translations system altogether
[11:06] <Nikerabbit> nope, first you remove the tags, then you go to Special:PageTranslation to unmark the page, and then you go and delete all the related pages manually