Assuming this task is about all wiki-facing error pages (including non-mediawiki 404s and all errors listed at T113114), this looks like a duplicate of T76560: Better WMF error pages.

The design for all these error pages would be based on the outcome of T110376.

@Krinkle I agree. and even the blocked tasks here have a lot of overlap.

T76560: Better WMF error pages
T22079: Provide a better means of status update delivery in WMF error message

@Krinkle @Nirzar As far as I have understood, there are error pages that we can't touch right now or at any time soon, mostly for technical reasons. Therefore T113114 started as a sub-set of error pages, we can address with a baseline in design and hopefully lots of overlap in code. Correct?
As T110376: Evaluate usability of the non-MediaWiki 404 page is about evaluating 404 as most prominent page, this task here was meant to separately collect, discuss and solve best-possibly the design challenges for the new baseline design for all errors at T113114. A better, clearer title is welcome.

In T129433#2113160, @Volker_E wrote:

As far as I have understood, there are error pages that we can't touch right now or at any time soon, mostly for technical reasons

No, we can change any / all of them.

@Volker_E
Taking DR off this again: not assigned to us, not necessarily within our remit (as scoped), but please feel free to re-add us if you require design research resources related to this project.

Reducing maintenance overhead is appreciated work, but let me point out that the main issue with the current error pages is that they are English-only. Until that's fixed, everything else feels like make-up to me.

In this regard,

This is also bad: https://la.wikisource.org/w/aaaaaa, https://la.wikipedia.org/w/aaaaaa, with hard-coded English text and even an English Wikipedia URL:

Alternatively, you can visit the <a href="/">Main Page</a> or read <a href="https://en.wikipedia.org/wiki/HTTP_404" title="Wikipedia: HTTP 404">more information</a> about this type of error.

In T113114#3153185, @Nemo_bis wrote:

IMHO the consistency was made in the wrong direction. All error pages should have followed the multilingual design.

The translations were at least 5 years out of sync with the English versions, and that was before we moved from SVN to Git. Since then the messages have changed various times more in the 3 years that followed. I've tried to trace where any of these come from but I gave up after 2 hours. Yes, these should be localised, but we first need a way to facilitate that in a maintainable fashion. translatewiki.net seems like the natural choice.

A few things to consider:

• Create a repo and import messages from current error pages. (Should be fairly simple now that T113114 is fixed.)
• Set up translatewiki.net integration for this repo.
• Decide how to localise the error page: Client-side with JavaScript, or server-side (e.g. based on subdomain or Accept-Language)?
• Create a build script in mediawiki-config or operations/puppet that we can use to re-generate the error pages based on the current localisations. If method is client-side, the build script would substitute a JSON object as part of a <script> element. If method is server-side, the build script would create variations of the file based on language code (e.g. errorpages/404.en.html).

I repeat what I said in another ticket that was way closer to this one:

In T113114#5136922, @Ladsgroup wrote:

Just a wild idea, lots of websites have a fun tone in their error pages (both for 404 and 500). I have seen youtube referring to chaos monkeys, the north face says your page is eaten by a goat, github refers to star wars. I personally think If we do this, it reduces tension caused by frustration of the best website in the world not working. Does anyone think we should do it? If yes, I make another ticket for that.
Some examples: https://rigor.com/blog/15-awesome-fail-pages

(We should think of not just 404, but also 500s too)

Popping in an idea - it would be cool to have the WMF explore partnerships with missing children organizations, to display "missing" notices of such children. Something I stumbled upon today was https://notfound.org/en, which I think is quite a cool idea, and the play on words is nice.