I am not sure about the differences, I just know that it is recommended to use them when using the Better BibTeX plugin for Zotero, I think it's only finetuning of the CSL JSON format.
Here is some linke regarding Better CSL and Better BibTeX for Zotero.
Maybe it can be of help and interest for your project.
It is great that you are making this plugin for Joplin.
Better BibTeX for Zotero :: Better BibTeX for Zotero (retorque.re)
this explain some of it:
Bundled translators :: Better BibTeX for Zotero (retorque.re)
github:
retorquere/zotero-better-bibtex: Make Zotero effective for us LaTeX holdouts (github.com)