In this new age of globalised accounts, users look at local wikis for the availability of account names for new accounts or renames, and often the username is not in use locally, but it is in use globally, so not available.
Users are instead pointed to global account [[Special:GlobalUsers]] which is
* butt ugly
* slow and not useful, especially as it does not manage anti-spoof, and it displays in coding sort, not human logical sort
We need a search tool at each wiki that allows a user to test the availability of their (chosen|selected) username against the database with anti-spoof matching in place. Thinking NOT against title blacklist as that would make things to easy for the trolls. Whether we wish to give clues of usefulness or conflicts is a separate issue. Whether we wish to offer availability of account names where there choice is not there, is a separate (later) matter.
We need an easy means in the users' languages to run this search so they can find a rename target, and this is before they get to the rename request pages.