Mastodon "translate" feature does not work on image captions

[mcclure]

Pitch

Consider this post:

https://mastodon.social/@NuOpRadio2@mastodon.nl/109978313750597984

It's in Dutch. It has an image attachment with a caption; the post is a little hard to understand without having either context or the descriptive text in the image caption.

I can click "Translate" and it translates the text to English. But if I mouse over the image attachment, it remains in Dutch.

Motivation

If a user wants to read the post text translated it stands to reason they'd want the image captions translated, especially if they are nonsighted.

[mcclure]

It looks like this

[mrfoogles]

This sounds like a good idea: trying to read german servers and so on the translate button is very useful, especially if you want to try to read some and translate others.

Special case, that might be added:

• For image-only posts, maybe the "translate with deepL" button should say "translate caption with deepL" instead, for clarity. I don't know if there are many posts with english text and dutch captions, but this would also work with them.

[mrfoogles]

For anyone trying to do this, I looked at the code, and I think you'd have to modify:

• The "/api/v1/statuses/{id}/translate" endpoint to return the caption translation
• The code to create the data structure for status that is stored in the Redux state (the one that Status and StatusContent use in their props): the translatable field would have to be updated to be set to "yes" if even the alt-text for the image was translatable.
• The MediaGallery and Video classes to take translations for their "alt", or caption, fields
• The Status class to pass the translations to them.

[renchap]

Fixed in #24175