I can't reproduce the issue. Which wiki did you use to create the temporary account? English Wikipedia replaced the link to point to a local help page https://en.wikipedia.org/wiki/Special:AllMessages?prefix=temp-user-banner-tooltip-description-learn-more&filter=all&lang=en&limit=50 (as did some other large wikis, e.g. dewiki). Your home wiki zhwiki still uses the original message https://zh.wikipedia.org/wiki/Special:AllMessages?prefix=temp-user-banner-tooltip-description-learn-more&filter=all&lang=zh&limit=50 which directly points to https://mediawiki.org/wiki/Special:MyLanguage/Help:Temporary_accounts

Sorry for the misleading URL. The English Wikipedia link was made up - I only tested it on some wikis that didn't customize the message like zhwiki and meta.
Yes, in the message source code, it used [[mw:Special:MyLanguage/Help:Temporary_accounts|XXX]]. The issue is that, given that wikitext, it's parsed as the wrong link (/wiki/Mw:...) when it is actually shown in the tooltip.

I don't really get the issue reported here.

In T418683#11661083, @Leo768 wrote:

Yes, in the message source code, it used [[mw:Special:MyLanguage/Help:Temporary_accounts|XXX]]. The issue is that, given that wikitext, it's parsed as the wrong link (/wiki/Mw:...) when it is actually shown in the tooltip.

In what circumstances did this happen? The interwiki link actually works even on non-WMF wikis like Miraheze.

FWIW I imagine that something like this could potentially be an issue for wikis that have disabled the mw: interwiki (which IIUC is a valid thing that can be done); see also e.g. T240811#9852582

In T418683#11661091, @Dragoniez wrote:

In what circumstances did this happen? The interwiki link actually works even on non-WMF wikis like Miraheze.

That's because Miraheze enabled "forward" for the "mw" interwiki prefix.

In T418683#11661101, @A_smart_kitten wrote:

FWIW I imagine that something like this could potentially be an issue for wikis that have disabled the mw: interwiki (which IIUC is a valid thing that can be done); see also e.g. T240811#9852582

No, it's about the "forward" field in Special:Interwiki. See also Manual:Interwiki_table#iw_local & Help:Interwiki linking#Non-local interwikis. In the default config, "mw" does not have "foward" enabled.

As that message is loaded by JavaScript, it shouldn't use interwiki links (all interwikis are non-local by default). It should be changed to a normal external link.

This will be affected by our changes to remove the grey bar T417371: Replace/remove the gray bar temporary account holders, but AFAICS the link will still exist

This problem comes up from time to time in different components, and I just saw T377640: Going to a non-local interwiki directly should display the same thing as GoToInterwiki. today, which suggests a partial but generalized solution to the problem: just make the link work, but require clicking through a confirmation screen. We already use that in other cases, e.g. when you input the interwiki link into the search box. I'd welcome some opinions from y'all on that ask, but it seems like a good idea to me.

Change #1271932 had a related patch set uploaded (by Dreamy Jazz; author: Dreamy Jazz):

[mediawiki/core@master] Temp accounts: Make "learn more" link use standard help page

https://gerrit.wikimedia.org/r/1271932

Change #1271932 merged by jenkins-bot:

[mediawiki/core@master] Temp accounts: Make "learn more" link use standard help page

https://gerrit.wikimedia.org/r/1271932