Narrowing the request to the case explained above and moving to i18n in order to gather the atention of maintainers sensitive with multilingual content.

So, any page content or UI component that uses wikitext for output can use <span lang="en">blah</span> already.

As I understand the problem is that folks would like to do this in messages that are plaintext...

Possibilities include:

• change those messages from plaintext to wikitext (are there performance issues, or issues with being able to render things for JavaScript client-side usage?)

• add a new message format that does some kind of restricted HTML, use that in place of plaintext/wikitext/raw HTML.

• ???

Functions of XML and Html classes don't accept message objects. Currently it is all or nothing escaping there.