I use PotPlayer, which can show two subtitles at once; also, when you click on a word, it can search it in the search engine of your choice (e.g. a dictionary). You can also add multiple search engines (as well as "Copy to clipboard" command) accessible when you right click a word instead of left clicking. You can also assign a shortcut (e.g. Ctrl+C) to copy the whole subtitle visible on the screen, to paste in Google Translate etc. I use all of those features, and it significantly helped in my English learning in my teens (and later other languages).

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).