The corresponding change is https://gerrit.wikimedia.org/r/#/c/177973/

https://ja.wikipedia.org/w/index.php?title=MediaWiki:Lastmodifiedat&oldid=23775446 was also affected. This customization was for informing the timezone (UTC) of the wiki and giving links to explain further.

Ugh, obviously I should have checked for this and give time to fix these. Nevertheless, we should migrate away from raw html. I think that if we allow using wikitext here, most if not all of the linked examples can be re-implemented.

I think it's good to avoid HTML in this message (shown on every single page) before its usage spreads further (similar to MediaWiki:Copyright which has become practically unfixable). Let's parse wikitext here and then inform (+ apologise to) all affected wikis.

@Jackmcbarn, I see you deleted the message on some of the affected wikis, do you know how many are left? I see about 120 which created this page, but most of them are old translations in need of deletion.

Change 191333 had a related patch set uploaded (by Whym):
Passe "retrievedfrom" and "lastmodifiedat"

https://gerrit.wikimedia.org/r/191333

Patch-For-Review

Change 191333 merged by jenkins-bot:
Parse "retrievedfrom" and "lastmodifiedat"

https://gerrit.wikimedia.org/r/191333

In T86702#985086, @Nemo_bis wrote:

@Jackmcbarn, I see you deleted the message on some of the affected wikis, do you know how many are left? I see about 120 which created this page, but most of them are old translations in need of deletion.

No idea.