Previously I used KMPlayer by the same developer, which supported not just two but three simultaneous subtitles (which I sometimes used, as strange as it may sound); but I switched to PotPlayer when he sold the program and it started to be bundled with ads.
Both programs are only available on Windows, and lack of something as featureful and customizable as PotPlayer was one of the reasons my brief flirtation with Linux at the start of this year wasn't that satisfactory. But if all you want is multiple subtitles, I found SMPlayer on Linux that did the job; but the features of PotPlayer/KMPlayer is simply unmatched (beyond just language learning).
never mind the 'anime' in the name, it's just a web video player that supports nearly every format and has good subtitle integration.
you'll need a hover/popup dictionary (for example, for Japanese Yomichan is popular) to go with it
I've been learning japanese for nearly a year using yomichan[0] mpv, mpvacious[1], and anki[2].
There is a fair bit of setup involved: https://www.youtube.com/watch?v=bbg6ztWecbU&t=0
[0] https://foosoft.net/projects/yomichan/
Haven't tested it in a while.