youtube-auto-select-original-audio-language.user.js

// ==UserScript==
// @name        YouTube Auto Select Original Audio Language
// @namespace   https://greasyfork.org/en/users/85671-jcunews
// @version     1.0.1
// @license     AGPL v3
// @author      jcunews
// @description Context: https://old.reddit.com/r/CodingHelp/comments/17aadka/youtube_pick_a_language_option_on_page_load/
// @match       https://www.youtube.com/*
// @grant       none
// ==/UserScript==

(rx => {
  rx = /original/i;
  setInterval((e, a) => {
    if (e = window.movie_player) {
      a = e;
      while (a?.tagName) {
        if (getComputedStyle(a).display === "none") return;
        a = a.parentNode
      }
      if ((a = e.getAvailableAudioTracks()).length && !rx.test(e.getAudioTrack().Qc.name)) {
        a.some(o => {
          if (rx.test(o.Qc.name)) {
            e.setAudioTrack({id: o.id});
            return true
          }
        })
      }
    }
  }, 200)
})()