Create a password blacklist located at MediaWiki:PasswordBlacklist so that users cannot use simple passwords such as 1234, password, or other weak passwords.
This is an insufficient solution to a valid problem. Hence I am declining this task. Password strength nowadays is mostly defined by a minimum number of characters, requiring capital and non-capital case, numbers, other symbols, etc. Not by fiddling around with some blacklist.
Password strength is totally defined with blacklists nowadays, but a wiki page is not sane storage for that. FWIW we now have a Composer package (wikimedia/password-blacklist) which packs the top 100K common passwords into a Bloom filter. See $wgPasswordPolicy on how to use it.
(Apologies for poking at old tasks but this is the top result when searching for "mediawiki password blacklist" so I figured it's helpful to have a pointer here.)