Uhm, this might be a little insensitive, but why not just write comments? That would be understandable by everybody, including blind people who would be excluded with sign language videos.

This sounds to me as convenient as making a comment as an audio recording. Ie not at all.

That said, video capabilities are constantly improving. But as most instances are run and financed by volunteers, adding video uploads would greatly increase the disk space requirements. So I guess you would need a specialised instance to host the videos that would have to be policed so that the feature wouldn't be abused to host illegal videos or porn.

Lemmy isn't the best in regards to a deaf community when compared to Mastodon that has accessibility built into the community values. But it, as far as I know, has the ability to do what you ask should the admin allow it. For that reason, I would suggest starting an instance, that way you can support video uploads, etc. Worst case scenario, you'll have to host your videos on a third party service.

You can link to videos in comments for sure.

Uploading to your instance could be a problem though. Video is data intensive, even with short clips. There's really no support for uploading videos in comments anyway, but it really wouldn't be sustainable long term.

But, linking to an external video host is easy peasy! Otherwise, you gotta write like us plebes :)