I would love to propose a 3rd way:

• Move the existing page to https://www.mediawiki.org/wiki/Extension:FileImporter/Introduction_to_configured_wikis or something like this.
• Remove the PrefixIndex line from the source.
• Do not turn https://www.mediawiki.org/wiki/Extension:FileImporter/Data into a redirect. Instead, replace it's contents with {{Extension:FileImporter/Introduction to configured wikis}}{{Special:PrefixIndex/Extension:FileImporter/Data/|stripprefix=1|hideredirects=1}}.

In T256623#6268106, @thiemowmde wrote:

I would love to propose a 3rd way:

Excellent! Let's do that one.

Uh, I just realized, is it even possible to transclude a page with localizations so that the localizations still work? Maybe it's better to stick to suggestion number 2 then.

In T256623#6271382, @thiemowmde wrote:

Uh, I just realized, is it even possible to transclude a page with localizations so that the localizations still work? Maybe it's better to stick to suggestion number 2 then.

Good catch! T47096: Add a way to transclude template or other page in the correct language: open, "high priority". There's a new WIP patch...

I've asked for the "Translation Administrator" group membership on mediawiki.org.

The page and its translations has been moved, so the configuration subpage list is cleaned of all translation subpages.

To demo: visit https://www.mediawiki.org/wiki/Extension:FileImporter/Data

Follow-up is to point to the redirect target from configuration.

Change 609748 had a related patch set uploaded (by Awight; owner: Awight):
[operations/mediawiki-config@master] Update help URL

https://gerrit.wikimedia.org/r/609748

Change 609748 merged by jenkins-bot:
[operations/mediawiki-config@master] Update help URL

https://gerrit.wikimedia.org/r/609748

Mentioned in SAL (#wikimedia-operations) [2020-09-07T11:27:21Z] <urbanecm@deploy1001> Synchronized wmf-config/CommonSettings.php: ff9f1042529bd332effc0fcd18db70f417c2e939: Update help URL (T256623) (duration: 00m 56s)