This is a tip for those who would like to display 2 (or more) subtitles while watching a video using a software player on your PC.
This option comes handy, for example, when you would like to compare translations, side by side, while previewing a video.
This is also very useful way to improve knowledge of foreign spoken languages, specially for kids who would be interested in it, while watching their favorite DVDs.

Software:
PowerDVD
Nero ShowTime
KMP player

DVD video

1. Every user of PowerDVD knows that it will display the second subtitle track if you right click on a playing DVD video and choose Subtitle>Secondary subtitle and choose the second subtitle to be displayed (if there are multiple subtitle tracks in DVD, of course).

2. New version of Nero ShowTime can load and display external subtitles in .srt and .sub format while watching a DVD or .avi video file.

3. But there is an option to display up to 3 external subtitles tracks on a DVD video using the KMP player. Those external subtitles should be in .srt format. To open a DVD video with KMP player, open KMP, right click and choose Open file, then go to Video_TS directory of a DVD and click on the first .ifo file. Play a video and then right click on it, choose Subtitles>Load Subtitle and find your first .srt file to load. Then go again to Subtitles>Subtitle languages>2nd subtitle and choose your second .srt file to be displayed. Repeat this if you want 3rd subtitle to be displayed.

AVI, MKV, MPG

1. using the KMP player and the procedure described above (2), you could display up to 3 .srt format subtitles while watching an .avi, mkv, mpg video files. Besides, there is an option to choose single, multiple or ALL subtitles which are inside the .mkv container. The same works with .idx/.sub subtitle files.