Youtube and Dailymotion videos can have external subtitles (closed captions). External means they are not the part of the video frame image. So they can be turned on and off, and video can have multiple subtitles.
On Youtube in addition to regular subtitles are also available two other kinds of them: auto-generated (using speech recognition) and auto-translated (machine translation of one of regular subtitles or auto-generated one, available only if video has some of them).
Filter uses Criteria to fine-tune which subtitles to use. It is configured using option
General Quality Subtitles.
All selected subtitles are downloaded at video opening stage. So the more subtitles are selected the longer it will take to open a video.
If subtitles were downloaded they should be available via standard way to select subtitles for the player (example).
Help Subtitles support