I know this is an old thread, but still one of the top results in Google when looking for this problem.
I'm just writing to explain how I solved it, and hopefully it'll help others.
1) Install the required software
* Latest version of
VLC
* Mederi's
"Subtitler (lite)" VLC extension (
link)
*
Key Presser (
link from softpedia)
2) How to make it work:
* You need the
secondary subtitle in srt format (primary subtitle can be embedded in the mkv or mp4 file of choice), name it exactly the same as your video file and put it in the same folder.
* Start video play in VLC, choose your primary subtitle (displayed bottom), and click View -> Subtitler Lite (Mod); A Window with a "Refresh" button will appear.
* Start Key Presser, choose "Subtitler Lite (Mod)" in the application list, Single Key "Enter", Time Interval of choice (I use 100ms), and click "start".
And there you go, your video should play showing both subtitles (top and bottom) simultaneously.
Now here is still hope that some future version of VLC has native support for multiple subtitles. There is an increasing number of multicultural households around the world, and this is a much needed feature.
PS: I've tried so many alternatives I can't remember, anything from KMPlayer (sometimes works, but it's terrible buggy and full of crapware/adverts), good old BSPlayer (supposed to work but fails to display subtitles in modern mp4 files), etc. Also saw some people were joining two srt files together, which is a viable alternative if you have them, but not really if you need a subtitle stream with non-latin complex characters (Japanese in my case), for which OCR is terrible and srt files are not available (only vobsub style bitmaps).
Now what I wrote above is far from being an elegant solution, but it works seamlessly and uses only free/open software.