Although the Wikimedia Developer Portal is a great entry point for people interested in Wikimedia technical projects in general, this page should also provide a link to the developer documentation specific to MediaWiki. Instead of linking to both Manual:Contents and Developer hub, as this page did previously, I'd suggest linking to just Developer hub since it is more comprehensive and includes a link to Manual:Contents.
Proposed change:
<h3><span class="header_icon" aria-hidden="true" role="presentation">[[File:OOjs UI icon chem.svg|20px|middle|link=]]</span><span><translate><!--T:3--> Develop and extend code</translate></span></h3> <div id="mainpage-devs" title="<translate nowrap><!--T:15--> Developers</translate>" class="items"> * <translate>Read the MediaWiki [[<tvar name=1>Special:MyLanguage/Developer hub</tvar>|developer documentation]]</translate> * <translate><!--T:41--> Visit the [<tvar name=1>https://developer.wikimedia.org</tvar> Wikimedia Developer Portal]</translate>