I have very good news for the developers, who are using Github to host projects with InterSystems ObjectScript. Github introduced the support of InterSystems ObjectScript this week!
How does it work?
All the credits go to @Dmitry Maslennikov, who is developing VSCode ObjectScript module and code highlighting of VSCode and Github both use TextMate grammar. Dmitry had introduced the PR to Github Linguist which was reviewed by the Github community and has been recently approved.
So your repositories with cls will no longer go as strange Apex or TeX but as InterSystems ObjectScript.
Thanks, Dmitry! Hope you'll provide the details on how ObjectScript is supported in Github.