I create video files using Kdenlive and then burn them to DVD using DVDstyler. No problem.

Using Kdenlive, I can generate subtitles which are automatically added to the image - but that means that the subtitles are 'always on'.

I believe that I can export the subtitles (from Kdenlive), so that I can have the video and subtitles as separate files.

I see suggestions that DVDstyler can write DVDs with subtitles which are selectable - but I am not clear on how to do it.

Is there any good documentation on adding subtitles using DVDstyler?

I have progressed.

First, I exported the subtitles from Kdenlive (to a .srt file) .

Then, having added the video to my DVD in DVDstyler, I double-clicked the video and could add the subtitle file. There is an option to "Force Display" which does not seem to make any difference.

I make the DVD and, using the preview option with VLC Media Player, I can play the DVD and I can select to show the subtitles. I have a number of 'titles' on the DVD. If I 'Play All', when play reaches the video with the subtitles, the subtitles appear bold and black. See attached screenshot. If I choose 'Select Title' and turn on subtitles, the subtitles appear NOT bold and with yellow fill and black outline. See attached screenshot.

I don't know what causes the different appearance.

Attached Thumbnails

   

Here is my process for creating a DVD which has clips with subtitles which can be turned on or off as desired. I use kdenlive and DVDstyler.
In kdenlive, import the video which is to have subtitles. Drag it into the timeline (starting at 0).
At the top of the timeline, just under the timing numbers, at the left hand end (0) you will see a short pale blue line. Drag that out to select how much of the video you want subtitles for (quite likely, all of it).
Then select Project→Subtitles→Speech Recognition→Process. The subtitles will be generated. Then, Project→Subtitles→Export Subtitles, specify your filename and include the .srt extension.
You can now close kdenlive.
Optionally, open the .srt file with a text editor and make any corrections you feel appropriate to the text and save it again.
In DVDstyler import your video. Then, either double click on the video or right-click and select properties. In the top right of the properties window is a large green + sign. Select that and add the .srt file you created earlier.
Create your DVD in the normal manner and you should be able to turn subtitles on and off using your DVD player.

Thanks for the tutorial.
It seems likely to assist someone in the future.