Here is an excerpt from their site:
If you’re interested in adding subtitles to our YouTube videos, that would be awesome of you. Thumbs up.
Here’s the 411:
1. You will need to have your own YouTube channel and be signed in to be able to add subtitles.
2. Once you finish translating a video, the subtitles will automatically go into a peer review process before they are published. To learn more about that process: Read this.
3. We do have English transcripts available for a few of the videos, if that would be helpful to you in the translation process. You can find those here. If you don’t see a transcript for a video you’d like to translate, that means that we don’t have one yet! If you make one for yourself, feel free to send it in to us so that we can share it with others. (Overachievers are our favorite).
4. Ready to become a Subtitle Master? Click on the links below to add subtitles to that specific video.