We're reviewing source code in a language that is not currently supported by Collaborator (Ada). It would be useful to be able to add a language syntax highlighting definition. There are other tools,...
+1
https://highlightjs.org/ offers HTML support via JS for 135 languages and 65 styles. See https://github.com/isagalaev/highlight.js/tree/master/src/languages for complete list.
See https://highlightjs.org/usage/ for usage and how to integrate into app. For collaborator, this looks like it would integrate very well into your technology. Supports language extensions as well.