I want to configure a tool so that I can just call with a movie as an argument and automatically download the appropriate english subtitle by file hash or name. I recall I had something configured like that but now I don’t remember what was the tool I used.
In VLC, i use this extension called VLSub. It downloads subtitles from opensubtitles.org by hash or by name of the movie
Not exactly what you are asking but have you tried https://www.bazarr.media/
You can automate and forget about it
Maybe you are thinking of Subliminal which works by calling GuessIt to identify the video and then tries to find and download subtitles from various sources. There are plugins to use it automatically from mpv and probably other players too.
Edit: looks like most of the providers are broken so this doesn’t work very well anymore.
There are scripts for MPV that do this
You’d expect MPV was published by MIT or Bell Labs in late 1970’s because it is so good, can do literally anything while remaining lightweight. But no, it is released in August 2013.