Templates like Template:Lang on enwp are already widely used. Could this feature support such templates?
Topic on Talk:VisualEditor/Beta Features/Language
Support existing templates?
There are Lang, Langi (italicizing the text), Lang-xx (prepending the language name).
There is a problem though. One user reverted my mass addition of "lang" to a phrase repeated in an article, and said it was annoying especially with the VisualEditor. With templates, it is shorter in code, but in VisualEditor it appears with blue background when hovered (supposedly a generic “template” indication), and needs waiting or clicking to see the template name, and two clicks to see the attributes.
Maybe the editor could ignore such templates by default, so people not editing the tagged text would not be bothered by it?