Change 103649 had a related patch set uploaded by TTO:
Disable interwiki magic for wikimedia (chapter) sites

https://gerrit.wikimedia.org/r/103649

I recommend WONTFIX here:

• linking other subdomains of the same domain is a valid usecase in general and specifically for chapters (which obviously have links from one to the other),
• you didn't mention any actual problem you're solving except a testcase created by you,
• you didn't check how many pages you're breaking and it took me one second to find one (the first I checked) i.e. https://pl.wikimedia.org/w/index.php?title=Strona_g%C5%82%C3%B3wna&oldid=45292 (main page!).

(In reply to comment #2)

I recommend WONTFIX here:

• linking other subdomains of the same domain is a valid usecase in general

and
specifically for chapters (which obviously have links from one to the other),

Have you read what wgInterwikiMagic actually does? See [[mw:Manual:$wgInterwikiMagic]]. Basically, this change stops interlanguage links from appearing in the sidebar of chapter wikis.

• you didn't mention any actual problem you're solving except a testcase

created by you,

For an example, "Brezhoneg" link (Breton language) goes to Wikimedia Brazil site (written in Portuguese, nothing to do with Breton, so the link should not be titled "Brezhoneg", and should not really appear in the sidebar at all)

• you didn't check how many pages you're breaking and it took me one second

to
find one (the first I checked) i.e.
https://pl.wikimedia.org/w/index.
php?title=Strona_g%C5%82%C3%B3wna&oldid=45292
(main page!).

This does not use interwiki magic, aka interlanguage links in the sidebar.

Thanks; I'm still unclear about points 1 and 2 in comment 2 though.

Let me explain some more:

• linking other subdomains of the same domain is a valid usecase in general

Of course it is, and this bug won't change that. Non-broken chapter sites will not be using sidebar interlanguage links, since they are the wrong way to interlink chapter sites. The correct approach would be sidebar interproject links (bug 708), but since they don't yet exist, inline links are the next best thing.

• you didn't mention any actual problem you're solving

I'm being proactive here. I read the rationale for WMUK's decision to move away from their WMF-hosted chapter site, and some of the reasons given were long-standing bugs that had not been fixed for years. If we want chapter wikis to hang around in the WMF cluster (it's cheaper for them to do that), then we should be trying to iron out all the bugs. In particular, there are lots of things wrong with interwikis on chapter wikis, and this is but one of them.

Hope that helps you to understand this.

Change 103649 merged by jenkins-bot:
Disable interwiki magic for wikimedia (chapter) sites

https://gerrit.wikimedia.org/r/103649