For several years, I was wondering how to make Mediawiki search case insensitive. I didn’t really had time to look at it until I was really fed up. That’s why after a few seconds of search, I’ve found an extension for Mediawiki which is working perfectly called TitleKey.
The TitleKey extension provides a case-insensitive title prefix search. It uses a separate table for the keys, so if it works cleanly it can be deployed without an expensive rebuild of core tables, and dumped when Wikimedia gets a nicer backend through Extension:LuceneSearch (pre 1.13) or Extension:MWSearch (1.13+).
For the average site administrator, the benefit of this extension is that it allows search suggestions (e.g. from Opensearch API) to be case-insensitive.
I’ve installed it to my wiki if you want to test 🙂