How to add a new file type which is similar to an existing type

[carlca]

I speak of Mojo which is a new language - https://www.modular.com/mojo - and is a superset of Python. Syntactically it is very similar, and to be honest, just a conversion of the .py scheme would be enough, but with the addition of the new fn keyword, alongside the existing Python def keyword.

I'm conversant with a range of languages and IDEs - just tell me what to do, and I should be able to do it!

[carlca]

I've tried using mdls list.mojo and then inserting the kMDItemContentType into the QLColorCode.qlgenerator .plist.
This resulted in a window being produced when the space bar is hit, but unfortunately the window is all white - no discernible text whatsoever! Any ideas?