Captionfy provides a subtitle editor that allows anyone to add captions to any Youtube video (even if they don't own the video) in any language. Once a user publishes captions to a video, anyone who needs it can watch the video on Captionfy with subtitles.

Captionfy is an advanced subtitle editor for YouTube videos.
Add colors to YouTube subtitles and easily fix auto-generated captions.
Anyone can help captioning your videos, or you can DIY. Many YouTubers ask their viewers for help with their subtitles.