It used to be quite hard to get an actually actually unmodified disc image.
A "good" remux is actually the highest quality movie release available, usually, if you don't care about file size. A good remux will combine all the best parts of every possible release into one super-file. For one movie, you could have the best video quality be on a French UHD Blu-ray, the best audio quality from a different source, subtitles aggregated from various international releases and streaming platforms (and filtered/deduped for quality), chapter titles taken from an old DVD, and all available commentary tracks collected. Rarely you might even see a hybrid release where multiple streams are spliced together to fix some problem or another in one of them. You can look for releases by the CINEPHILES p2p group for gold standard examples, they get distributed fairly widely so you can probably find some.
To answer what you asked about extra audio tracks specifically (outside of full disc images)--usually non-English dubs are considered bloat and aren't distributed. Commentary tracks are kept. Audio description is a mixed bag, good groups will keep it.
VC-1, H.264 (MPEG-4 AVC)
Also, the studio paid a professional to peep at all the inter-frame pixels and turn the knobs right when they encoded the bluray. I might be able to get a perceptually lossless rip that's 25-50% smaller than the original, but it's just not worth my time.