On enwiki, I tried to block 67.218.119.128/26. When I clicked the Block button, I got to a page with the error:
67.218.119.128/26 (talk • contribs) is already blocked (block log • unblock) .
which includes a link to:
https://en.wikipedia.org/w/index.php?title=User:$&action=edit&redlink=1
Note the "User:$" part.
This is English Wikipedia error from customization of this message. The original message does not even have a link.
<div class="alreadyblocked" id="alreadyblocked" style="color:red; font-weight:bold; font-size:96.75%;">[[User:$|$1]] ([[User talk:$1|talk]]• [[Special:Contributions/$1|contribs]]) is already blocked (<span class="plainlinks">[//en.wikipedia.org/w/index.php?title=Special:Log/block&page=User:$1 block log] • [//en.wikipedia.org/w/index.php?title=Special:IPBlockList&action=unblock&ip=$1&wpUnblockReason=unblock%20to%20change%20duration unblock]</span>) .</div>
You need to change [[User:$|$1]] to [[User:$1|$1]]
Fixed in https://en.wikipedia.org/w/index.php?diff=1012953676. Been broken since 2011.