It should be possible to merge your mkv with other official SEE Blu-ray audio to customize language…
Yep, languages should be pretty easy for anyone to add. Although, you’d probably want to do that with V2, since all the official Blu-ray releases are split into two parts. Then, you can merge the two parts together if you want it as one file.
Also, if you have any languages that you want added to a future release, feel free to send them to me. I already have German and Italian that I’m planning to add to the next release, which will hopefully be sometime in the next few months. (Just waiting on a request to be filled to get a NTFLX WEB-DL of Fellowship first). 😃