sign languages are completely different languages from spoken languages, with their own grammar etc.
subtitles can work but it's basically a second language. perhaps comparable to many countries where people speak a dialect that's very different from the "standard" written language.
this is why you sometimes have sign language interpreters at events, rather than just captions.
there's not really a widely accepted written form of sign language.
> subtitles can work but it's basically a second language
That argument applies just as equally to sign language - most countries have their own idiosyncratic sign language. (ASL, LSE, etc.). Any televised event that has interpreters will be using the national language version.
The closest thing you're thinking of is IS - International Sign but its much more limited in terms of expression and not every deaf person knows it.
> there's not really a widely accepted written form of sign language.
Because it makes no sense to have it unless there was a regional deaf community that was fluent in sign language and also simultaneously illiterate.
https://www.reddit.com/r/NoStupidQuestions/comments/6t7k1w/h...
>this is why you sometimes have sign language interpreters at events, rather than just captions.
No, the reason is because a) it's in real time, and b) there's no screen to put the subtitles on. If it was possible to simply display subtitles on people's vision, that would be much more preferable, because writing is a form of communication more people are familiar with than sign language. For example, someone might not be deaf, but might still not be able to hear the audio, so a sign language interpreter would not help them at all, while closed captions would.
if you're maximizing accessibility you'd have both. often in broadcasts with closed captioning, there will also be a video of the sign language interpreter.
Sometimes the captions miss things or are really terribly written.