Project Threepio is based on the original stereo/surround mixes. It does not make any attempt to accommodate later audio revisions (85 mix, 93 mix), it does not attempt to match the dialogue on foreign dubs (i.e. the translations can be different), nor does it include alternate crawl translations for the 81 video revision.

The mono mixes are a bit special, since they are original, so Project Threepio includes subtitles for the mono mixes of Star Wars and Empire (16mm), but only in English, and only in SRT format. I don't plan to do subtitles for the 70mm/8mm audio for Empire, even though that's also a unique original mix.

Future versions of Project Threepio will include a way to align foreign subtitles to the timing of the mono mixes, although it still will not include translations of the different lines.

Anyone who wants to use Project Threepio with a mono mix can do it, but there's some manual work involved. It's doable, but it doesn't work out of the box.

Direct other questions to the Project Threepio thread. This little question can go way down the rabbit hole in so many directions.