Some MediaWiki extensions are missing the license-name field in the file extension.json or in $wgExtensionCredits. This means no license is shown for them in Special:Version (e.g. https://en.wikipedia.org/wiki/Special:Version) or the license is displayed as 'License', instead of something like for example GPL-2.0-or-later.
To fix this, we need to make changes like https://gerrit.wikimedia.org/r/#/c/264553/ in the relevant extensions.
- Check the existing LICENSE or COPYING file of the extension to verify which license the extension has.
- Look up the corresponding value of that license in https://spdx.org/licenses/
- Add that value as the value of the license-name parameter to the file extension.json.
- Provide your patch for that extension in Wikimedia Gerrit. See https://www.mediawiki.org/wiki/Gerrit/Tutorial for how to set up Git and Gerrit.
Note that some extensions are possibly missing a LICENSE or COPYING file, which would result in a broken license link.
Note: the 'extensions' listed as wikibase or data values is outside scope of this task. Most of these are actually libraries and instead need to be moved to the libraries section of SpecialVersion. (see: T123937)