The messaging system doesn't really support formatting at the moment, which is why we haven't done this yet. There may be some hack we can do though.

Ping @matmarex

mw.message will do wikitext parsing, but ideally this would work in ve-core too.

In T195243#4220570, @Esanders wrote:

The messaging system doesn't really support formatting at the moment, which is why we haven't done this yet. There may be some hack we can do though.

To elaborate: MediaWiki's messaging system (mw.message + mw.jqueryMsg) does support formatting (it can treat the message as a HTML DOM tree, rather than just text), but the fallback system we use in standalone VisualEditor (jquery.i18n) does not.

In a perfect world, this would be as easy as replacing code like this:

return ve.msg( 'visualeditor-changedesc-changed', key, change.from, change.to );

With:

return mw.message('visualeditor-changedesc-changed', key, $( '<i>' ).text( change.from ), $( '<i>' ).text( change.to ) ).parseDom();

(We would have to do this in about 15 places for the descriptions for different elements, e.g. template parameter, link target, etc.)

Given the imperfect world we live in, I think we will instead need something like this, to construct the HTML string by hand:

return $( $.parseHTML(
	ve.escapeHtml( ve.msg( 'visualeditor-changedesc-changed', '$1', '$2', '$3' ) )
		.replace( '$1', ve.escapeHtml( key ) )
		.replace( '$2', '<i>' + ve.escapeHtml( change.from ) + '</i>' )
		.replace( '$3', '<i>' + ve.escapeHtml( change.to ) + '</i>' )
) );

(And probably some helper function for it, since it looks icky.)

Alternatively, we could try to make mw.message + mw.jqueryMsg a separate library independent of MediaWiki, or we could try to add the missing features to jquery.i18n, but either of these would be a major undertaking.

I'll have a look at this, we can probably do better than HTML building and create a method that supports DOM arguments.

Change 440664 had a related patch set uploaded (by Esanders; owner: Esanders):
[VisualEditor/VisualEditor@master] Create an 'htmlMsg' function for HTML messages with HTML or DOM arguments

https://gerrit.wikimedia.org/r/440664

Change 440665 had a related patch set uploaded (by Esanders; owner: Esanders):
[VisualEditor/VisualEditor@master] Use ve.htmlMsg to highlight values in attribute changes

https://gerrit.wikimedia.org/r/440665

Change 441028 had a related patch set uploaded (by Esanders; owner: Esanders):
[mediawiki/extensions/VisualEditor@master] Implement getHtmlMessage in mw.Platform and use for DiffElement

https://gerrit.wikimedia.org/r/441028

Change 441167 had a related patch set uploaded (by Esanders; owner: Esanders):
[mediawiki/extensions/Cite@master] Use getHtmlMessage for DiffElement

https://gerrit.wikimedia.org/r/441167

Change 440664 merged by jenkins-bot:
[VisualEditor/VisualEditor@master] Create an 'htmlMsg' function for HTML messages with HTML or DOM arguments

https://gerrit.wikimedia.org/r/440664

Change 440665 merged by jenkins-bot:
[VisualEditor/VisualEditor@master] Use ve.htmlMsg to highlight values in attribute changes

https://gerrit.wikimedia.org/r/440665

Change 441028 merged by jenkins-bot:
[mediawiki/extensions/VisualEditor@master] Update VE core submodule to master (a1fd90540)

https://gerrit.wikimedia.org/r/441028

Change 441167 merged by jenkins-bot:
[mediawiki/extensions/Cite@master] Use getHtmlMessage for DiffElement

https://gerrit.wikimedia.org/r/441167