Your requirements could not be resolved to an installable set of packages.

From semantic-mediawiki.org
< Installation‎ | Troubleshooting
Administrator manualInstallationInstallation/TroubleshootingYour requirements could not be resolved to an installable set of packages.
Composer issues "Your requirements could not be resolved to an installable set of packages" followed by "Installation failed, reverting ./composer.json to its original content."1
This issue appears for MediaWiki 1.29 and later when installing the respective point release from tarballs and issuing composer require mediawiki/semantic-media-wiki "~2.5" --update-no-dev. It can be mitigated by issuing composer update --no-dev first, e.g. composer update --no-dev followed by composer require mediawiki/semantic-media-wiki "~2.5" --update-no-dev.