Live Preview adds an empty "in other languages" section on the sidebar even if there are no interlanguage links on the page, or the wiki is not configured with interlanguage links.
The problem is in mediawiki.action.edit.preview.js which blindly adds that section of the sidebar.
Also, it's hardcoded for vector skin
The problem arise on pages using MediaWiki-extensions-LiquidThreads because it loads the mediawiki.action.edit.preview.js module (reported today on #mediawiki IRC channel)
This is easily reproducible on vector, enabling live preview on preferences, and previewing any page that doesn't have an interlanguage link.