Discourse uses highlight.js for its syntax highlighting. Though it might be a cut down version, I didn't check the current state. Highlight.js supports creating and submitting custom languages..
If a language definition for DOpus commands was created, would adding it to the site be complicated?
If it just involves adding some files to the server, we can definitely do that.
If it needs existing ones to be changed, we may be able to, depending on if the change can be done at runtime in js. (We already have our own Discourse plugin to change some other stuff so we can add to that, if it can modify things when it runs. Can't easily patch existing code on-disk as the changes will be lost each time the site is updated.)