If you are streaming a dvd, or an mkv file, then it may well have subtitles embedded in the file.
Otherwise, if your subtitles are in a separate file (like an srt file) then you need to name it correctly so that VLC can find it.
All you need to do is save the subtitle file 'next' to the movie and VLC will use it automatically when converting.
the srt file is in the same location as the movie, and has the same name (apart from the filetype).
you will need to delete and re-add the movie after putting the subtitles in the right place.
If there is only one subtitle or audio track, then it is easy, and by default, VLC Streamer will use it.
If there are multiple options, then you need to tell VLC Streamer which one you would like to use. You can set a standard preference in your helper app, or you can pick manually when you add the movie from the iPhone/iPad.
If you click on the 'advanced conversion settings' button in the 'add movies' tab, then you can pick your preference
You can see here that I have selected French as my preferred language for both the audio track and the subtitle track. This generally works well and is particularly successful with DVDs, however sometimes the tracks will not be labelled in a way that VLC can recognise, or there might be multiple tracks for a given language (e.g. a director's commentary audio track).
(note - at the moment, this method is not available on Android)
To pick the specific track, you need to add the movie from the iDevice, rather than adding it directly to the helper. To do this, click on 'add movie' in the main screen on your iDevice.
Once you have picked a movie, you'll get to the screen where you pick the quality setting. While you are looking at this, VLC is desperately trying to figure out what tracks are available for you to see. This might take 10s of seconds, or even a minute if your computer is very slow.
If VLC does detect tracks, then you'll see numbers show on the tabs at the bottom of the screen like in this image:
If so, then click on the tab and pick the track you want.
(Generally - this approach does not work for DVDs. I think the issue is that VLC looks for audio tracks in the menu screen, rather than in the 'main movie'.)
If you try converting the movie, and your subtitles look garbled, then there are two things you can check.
In the example below, the subtitle is encoded in Greek.
Changing the 'subtitle encoding' section in this case will make the subtitles work perfectly. In the case of this movie, I select 'Greek (Windows-1253)' - you may have to experiment to find the right encoding.
For subtitles in Chinese, Korean or other languages where there are lots of characters not included in the standard font, then you will normally see just squares for the characters. If you see this, then you can use the 'Custom subtitle font' option to pick a font which properly supports your language.
If you copied the movie by converting it in the helper and selecting 'copy to device', then all the comments above apply.
If you copied through iTunes, then VLC will try to play the movie on the device. It will still use subtitles, though you have somewhat less control. - Specifically, you can't control the encoding used for subtitles.
If you copied an mp4 or a mov through iTunes, then by default, VLC Streamer will try to play this in the system player. This doesn't handle subtitles. However - you can force VLC Streamer to play through VLC by tapping on the info button and selecting 'Play in VLC'
Hopefully this will help. If you have any comments or questions, then please post on the forum