Been trying to figure out how to do this for quite awhile. Finally found a program that can handle it, but unfortunately it’s windows only and GUI based, so doing it for a batch is difficult. Anyway, here’s the problem this sets out to solve:
For language learning purposes or because you want to watch something with a friend who doesn’t read the same language as you you want to watch a movie with subtitles from two different languages playing at the same time. We’ll assume the subtitles you’re working with are in SRT format, if they’re not the situation is quite a bit more complicated, you can check the suggestions below.
[EXPAND Suggestions for subtitles in other formats]
Your best bet is simply to get them into SRT format. You can find a lot of subs at subscene or opensubtitles (or just google) and save yourself the trouble of converting. If that’s not an option, then you can simply convert your subs to SRT format. The program we’ll be using below, Aegissub can import a wide variety of subtitle files, with the exception of vobsub (.idx/.sub extension subtitles).
If you have that kind of subtitle you’ll need to do an OCR conversion, do some googling for avidemux and/or vobsub.