I wonder if hacking subtitles would be harder than actually replacing the audio tracks with a fandub? I don't know, perhaps contact some famous fandubbing group to see if they're interested, I'm not too sure.
Both are usually equally difficult, though subbing is often plain impossible, because - unlike most other, later consoles - there's just one background layer and not enough space to sub things. That's one of the reasons as to why pretty much not a single PCE-CD game
was originally subbed, but rather dubbed instead. Also, I assume that in the US they just have more of a dubbing culture, which is not the case in every European country. Either way, anything cutscene-related on that console takes a significant amount of work... which is also probably why almost nobody does that.