Hey Andrew,
I'll check this out. I had originally tried to install Content Translation Manager and Filter and ran into a lot of different issues. We needed all translations to work with course backup and restore and all of the translation info available on a single page for a course (along with word count and character count). When I used those two other plugins, we would also lose the translations if the source language was updated (outside of the updatehash form). I don't know if those were configuration issues or use cases those plugins didn't support. Have you solved those with your filter?
Also, I gave up on the filter approach and decided to create something around mlang instead where a translator could go in, and work on the content for a single course:
https://github.com/jamfire/moodle-local_coursetranslator
Do you think that workflow would work with what you're working on?