Which of the Wikipedias was this tested with? Where/how to see "that the MediaWiki software is retrieving the default text from sister project Meta-Wiki"? Please see https://mediawiki.org/wiki/How_to_report_a_bug and provide steps to reproduce. Thanks!

In T203891#4569422, @Aklapper wrote:

Which of the Wikipedias was this tested with? Where/how to see "that the MediaWiki software is retrieving the default text from sister project Meta-Wiki"?

Mainly 'enwiki' (the English Wikipedia). It has the modified text, but is being rerouted to the default: m:MediaWiki:Globalblocking-ipblocked. As I stated earlier, when the 'Edit' or 'Edit this page' tab is clicked, and the IP address is globally blocked, the "View source for ..." page loads, bypasses the custom MediaWiki:Globalblocking-ipblocked system message to have the /qqq switch and displays the text differently, which looks identical to the original text for MediaWiki:Blockedtext:

View source for <page>

You do not have permission to edit this page, for the following reason:

Your IP address has been blocked on all wikis. The block was made by <steward> (<wiki>). The reason given is <reason>.

• Start of block: <block began on>
• Expiration of block: <date or infinite>
• Intended blockee: <IP>

You can contact <steward> or another administrator to discuss the block. You cannot use the "Email this user" feature unless a valid email address is specified in your account preferences and you have not been blocked from using it. Your current IP address is <IP>. Please include all above details in any queries you make.

Also, it's technically not possible to request a global unblock via m:Steward requests/Global since the globally blocked IP address cannot edit on all Wikimedia wikis, including Meta-Wiki.

Thanks for clarifying. That sounds like the default text is displayed, and no text from Meta-Wiki is pulled here.

I believe (but am not 100% sure) that this is a weird side-effect of the message override logic in WikimediaMessages. You should be able to specify that message in https://en.wikipedia.org/wiki/MediaWiki:Wikimedia-globalblocking-ipblocked (note the Wikimedia- prefix).