Manual:$wgCapitalLinks

Details
Set this to false to avoid forcing the first letter of links (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 piped link.

See also m:Help:Page name.