About [[MediaWiki:Visualeditor-beta-warning/en]]
Appearance
This message seem to be outdated. With the added possibility to switch to wikitext editing (using the menu option titled MediaWiki:Visualeditor-mweditmodesource-title/en you can get to wikitext and not losing changes).
Already reported via Bugzilla:57699. Nothing to do from translatewiki.net side currently. Anyways, thanks for your report.