A new interpreter is just like a new extension, but instead of the extensions folder you put it on the templates folder.
You can download it at the first link in this post:
The one annoying thing is that you have to put your sound files in twice. Once as .ogg files in the sounds folder in Materials (just like the inform book describes) and once as mp3s in an identical folder called sounds in the Release folder. It’s because the offline interpreters don’t use mp3s and Safari only uses mp3s. Sorry about that!