Manual:$wgCapitalLinks

Details
Set this to false to avoid forcing the first letter of page titles (including included pages, images and categories) to capitals.

WARNING: may break links! This makes links COMPLETELY case-sensitive.

Links appearing with a capital at the beginning of a sentence will not go to the same place as links in the middle of a sentence using a lowercase initial; typically the former has to become a link with a separate display title (e.g. page ).

After setting this to false, run  to fix the existing links that will be broken.