According to Siebrand on Gerrit change 31672, where we're trying to do a similar message overriding for Wikimedia sites:

I'm blocking merge for this, because conceptually there's something very wrong here. Can you please give this some thought, and tell me why this would work?

At this point the global blocking message says discuss with the blocking person. This is neither effective or productive when there is a large team of people acting as stewards at Wikimedia for 700+ wikis. Consider also that individuals come and go, so we may actually pointing people to a dead end (stewards do retire before their blocks end)

Stewards need to be able to have the ability to

• edit the message
• to display their message universally
• look to have a message in the local language (if volunteers will do so)

As Marco Aurelio has said we need the additional ability to include links to a specific page. I would add that we may be looking to add email links, as at the moment we specifically need to add that in the block reason and a default addition may be seen to be more effective.

Here the stewards see that pointing users/complainants to a central page, and/or to a universal email address (in OTRS) is a better systematic and responsive methodology. Having a better ability to globally configure a universal message/template is highly desirable. Giving stewards the tools to manage their affairs and information in real time (or close to) is the next step in maturing global block.

FWIW I am sure Krenair's comment is relevant, I just don't get the importance/relevance myself. I must be lacking a link to another information piece.

(In reply to comment #2)

FWIW I am sure Krenair's comment is relevant, I just don't get the
importance/relevance myself. I must be lacking a link to another information
piece.

Basically in that Gerrit change we tried to override a message (what this bug is about - but a different message) by setting it in the WikimediaMessages extension. But Siebrand -2'd it with a confusing message and has not elaborated.
It seems he thinks this should not work and that it should be done some other way, I don't know how though...

There should still be the right balance of local control, while still allowing stewards to send the message through.

Bumping this - I assume that siebrand's concern is that the normal way of achieving this in the WikimediaMessages module is to use a hook in core around the message that can be replaced by a WMF-specific message. You do not just over-ride the message with a conflicting definition.

E.g. the "hook" for "edit page copyright warning" allows MediaWiki:copyrightwarning to be replaced by MediaWiki:wikimedia-copyrightwarning as it calls a function ('efWikimediaEditPageCopyrightWarning') that returns that string instead of the default.

Thus, for centralauth-block-already-locked we should create a hook around that message and create a new message, wikimedia-centralauth-block-already-locked (or similar) that has the Wikimedia-specific aspects (in this case, the meta reference).

Does that make it clearer?

There's also a much simpler way to fix this, i.e. follow the usual MediaWiki approach as in

'searchresulttext' => 'For more information about searching {{SITENAME}}, see [[{{MediaWiki:Helppage}}|{{int:help}}]].',

Just replace "You can contact $1 to discuss the block." with: "For additional information and if you believe the block was made in error, see [[{{MediaWiki:Globalblocking-infopage}}]] or contact $1".
MediaWiki:Globalblocking-infopage should default to "Project:Global blocks", can be translated and can be easily overwritten with a link to Meta which will have specific instructions like "user SRG" or "write OTRS", see also https://meta.wikimedia.org/wiki/Talk:No_open_proxies#Instructions_on_appeals_and_translations

Remember also not to introduce bug 15259 with this message too; it seems it's fine now.

(In reply to comment #6)

can be translated and can be easily overwritten with a link to Meta which
will
have specific instructions like "user SRG" or "write OTRS", see also
https://meta.wikimedia.org/wiki/Talk:
No_open_proxies#Instructions_on_appeals_and_translations

The new process is ready for linking: https://meta.wikimedia.org/wiki/No_open_proxies#Global_exceptions_and_appeals
It will take a few days to wait for comments/objections and mark for translation, but a patch can now be worked on to link it.

Change 84343 had a related patch set uploaded by Nemo bis:
Add custom error messages to blocked users for global and Tor blocks

https://gerrit.wikimedia.org/r/84343

Change 84343 merged by jenkins-bot:
Add custom error messages to blocked users for global and Tor blocks

https://gerrit.wikimedia.org/r/84343

Fixed! Thanks Tyler for the code review.