Everything looks quite right to me.

I don't get it; it still happens with safemode=1, but I can't reproduce it on my bot account.

After tracing with the JavaScript debugger, it seems to be triggered by the mediawiki.action.edit.preview module, line 296. That explains why I only encountered on my main account; I have the preference Show previews without reloading the page enabled there.

I cannot reproduce it either but it seems like a bug that language links to wikipedia.org appear on mediawiki.org after an edit...

In T262374#6445790, @Mainframe98 wrote:

I don't get it; it still happens with safemode=1, but I can't reproduce it on my bot account.

After tracing with the JavaScript debugger, it seems to be triggered by the mediawiki.action.edit.preview module, line 296. That explains why I only encountered on my main account; I have the preference Show previews without reloading the page enabled there.

Note that actually I cannot reproduce it even with that preference checked. Not sure why.

In T262374#6447207, @Jdlrobson wrote:

...it seems like a bug that language links to wikipedia.org appear on mediawiki.org after an edit...

It seems like you're talking about two things. So for linking to wikipedia, that's intentional:

if ( in_array( $wgDBname, [ 'commonswiki', 'mediawikiwiki', 'metawiki', 'specieswiki', 'wikimaniawiki' ] ) ) { 		 
   $wgWBClientSettings['languageLinkSiteGroup'] = 'wikipedia';
}

But for the links appearing on action=edit may I am not sure, though that'd be a bug for MediaWiki-extensions-WikibaseClient then? Also note this is not specific to mediawiki.org

In T262374#6449864, @Ammarpad wrote:

But for the links appearing on action=edit may I am not sure, though that'd be a bug for MediaWiki-extensions-WikibaseClient then? Also note this is not specific to mediawiki.org

That was what the original bug report is about; I've clarified the reproduction steps to make this clearer.

In T262374#6449866, @Mainframe98 wrote:

In T262374#6449864, @Ammarpad wrote:

But for the links appearing on action=edit may I am not sure, though that'd be a bug for MediaWiki-extensions-WikibaseClient then? Also note this is not specific to mediawiki.org

That was what the original bug report is about; I've clarified the reproduction steps to make this clearer.

What about the title?

The "In other languages" portal appears unstyled when editing a page

(Note that in general, I get what you mean --see attached screenshot, I actually once noted it locally but it resolved itself on its own and I couldn't repro. For now too, I can't reproduce it either locally or on wmf wiki. That's my point. The image below is cut from old screenshot)

I don't think this is related to VisualEditor. I see the same issue on https://wikitech.wikimedia.org/w/index.php?title=Deployments&action=submit.

The issue is not in Vector but something trying to render a portal via JS which is currently not supported.

This is a regression because it used to work…

Change 626686 had a related patch set uploaded (by Ammarpad; owner: Ammarpad):
[mediawiki/core@master] Update Vector lang portlet class in js preview.

https://gerrit.wikimedia.org/r/626686

Change 626686 merged by jenkins-bot:
[mediawiki/core@master] Update Vector lang portlet classes in js preview.

https://gerrit.wikimedia.org/r/626686