You can get MediaWiki developer access

This is an invitation to get MediaWiki developer access.

https://www.mediawiki.org/wiki/Developer_access

With developer access, you can submit your patches right into MediaWiki
core and extensions, and comment on other people's changes.  We use the
Git source control system and we use Gerrit to review and merge commits.

https://www.mediawiki.org/wiki/Git/Tutorial

We encourage you to read the code review guide, so you can help review
code, and tips on getting your code reviewed:

https://www.mediawiki.org/wiki/Git/Code_review/guide
https://www.mediawiki.org/wiki/Git/Code_review/Getting_reviews

Also, if you would like to be a maintainer of MediaWiki core or an
extension, with the power to merge (or veto) changes, you can make your
case here:

https://www.mediawiki.org/wiki/Git/Gerrit_project_ownership

But anyway, if you don't have developer access already, just request it
and we'll grant it within a business day or so.  Thanks!
--

-- 
Sumana Harihareswara
Engineering Community Manager
Wikimedia Foundation