Is this being worked on or is it a low priority issue?
I don't really understand. Ch3vr0n had already stated, that MP4 doesn't support selectable subtitles. The MP4 file format simply has no provisions for that. That's nothing CloneBD could change.
The only possibility would be text subtitles, these are defined for the MP4 file format, but Bluray subtitles are graphics and that would require OCR text recognition to make it possible, which is currently not an option.
If you want selectable subtitles, you should convert to MKV instead of MP4.
Thanks again Pete, Im very satisfied by the product now. This was the only issue I had so far