I'm looking forward to seeing what you might do next, I really enjoyed "The Witch"!
This site has some nice shots of the filming of M, which show the camera used:
It looks like Lang used a Debrie Parvo L, which was probably the most popular studio camera in Europe then. I don't know how they recorded sound, since it looks unblimped.
Back in 1930 optics were at a pretty exciting point of development, with many old barriers being broken through. I think 32mm was probably still the widest focal length available for 35mm motion pictures - there were 32mm Tessars by Zeiss and Bausch & Lomb and a 32mm Cooke Opic (series 0), but 27, 25 and 24mm lenses by those same companies weren't far off.
Some surprisingly fast lenses had recently become available, such as the the initially f/2 Ernostar in the early 20s, (which led to the f/1.5 Zeiss Sonnar in 1932), a modified triplet. Paul Rudolph had developed the near symmetrical anastigmat Kino-Plasmat line for Hugo Meyer of Goerlitz in 1922, which got to f/1.5. And the most successful in terms of cinematography were the unsymmetric double Gauss designs such as the Cooke Opic (forerunner to Speed Panchro), Zeiss Biotar, Dallmeyer Super Six and Astro Tachar, which were f/2 or f/1.8.
Telephotos were also greatly improved, with the inherent pincushion distortion finally being reduced in the 20s, and fast designs made by firms like Cooke, Dallmeyer and Astro Berlin.
If you research Debrie Parvo L cameras, which date from the mid 20s to 30s, they do often come with Tessars, which were a highly successful 4 element Zeiss design dating back to 1902, but not particularly fast, only reaching f/2.7 by 1930. Sometimes they are Krauss Tessars, which were a French firm licenced by Zeiss. Focal lengths I've seen are usually 35, 40 or 50mm. It's likely these were "standard" lenses that were cheaper than the more exotic high speed or telephoto ones.
According to Raimondo-Souto's excellent "Motion Picture Photography" the best known optical firms in the field of cinematography at that time were Zeiss, Hugo Meyer, Schneider, Astro Berlin, Dallmeyer, Taylor Taylor Hobson, Ross, and Ermagis & Optis, along with Bausch & Lomb, Wollensak and Goertz in the US.
There is a Debrie Parvo L manual online that lists some of the high speed lens options available at the time (I would estimate it to be from about 1930):
Astro Tachar f/1.8
Atear Optis f/2 and f/2.5
Bausch and Lomb f/2.7
Ernostar f/1.2 and f/2
Kino Plasmat Hugo-Meyer f/1.5 and f/2
Krauss Zeiss f/2.7
..made in various focal lengths.
There is a picture of the camera fitted with an f/1.5 90mm Kino Plasmat, which is pretty fast even today! I can't vouch for the image quality wide open though..
Naturally none of the lenses had coatings at this point in time.