VisualEditor got the ability to edit language converter markup in T49411, but the implementation stopped short of hooking the new inspectors/etc up to the toolbar menu to allow users to insert new language converter markup from scratch. In particular the ability to add the "raw" markup -{ ... }- would be very useful.

(See also T182910: VE should support "hidden" and "describe" flags for language converter markup..)

There's a "Language" entry in the 'styles' drop down. Perhaps it could be made a nested menu, and allow variant markup as well as tagging the source language.