User script that replaces the twitter box denoting the image has ALT text with the real ALT text.

twitteralt.user.js

// ==UserScript==
// @name         Twitter show ALT text
// @version      1.0.0
// @author       1-UP Nuke
// @icon         https://abs.twimg.com/favicons/twitter.ico
// @description  Replaces the twitter box denoting the image has ALT text with the real ALT text.
// @match        https://*.twitter.com/*
// @grant        none
// ==/UserScript==
window.addEventListener('load', function() {
  setInterval(()=>{
      for(let span of document.querySelectorAll('span'))
      {
        if(span.textContent == 'ALT')
        {
          let altBox = span.parentElement.parentElement;
          altBox.style.maxWidth = '90%';
          altBox.style.height = 'max-content';
          span.textContent = 'ALT: ' + altBox.parentElement.querySelector('img').alt;
        }
      }
    },
    1000
  )
}, false);