点击一下即可开启中英双字幕,适用于YouTube™，改编自https://github.com/ADengrc/youtube-captions/

YouTube™双字幕.user.js

// ==UserScript==
// @license      MIT License
// @name         YouTube™双字幕
// @description  点击一下即可开启中英双字幕,适用于YouTube™
// @namespace    https://github.com/ADengrc/youtube-captions/
// @version      0.1.0
// @author       Dengrc （Adopted by Daniel.Zeng）
// @match        https://www.youtube.com/*
// @require      https://cdn.jsdelivr.net/npm/xhook@latest/dist/xhook.min.js
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    xhook.after(function (request, response) {
        let url = request.url
        if (url.includes('/api/timedtext')) {
            const zhReg = /^zh-\w+/
            const params = new URLSearchParams(url)
            let lang = (params.get('lang') || '').toLocaleLowerCase()
            let tlang = (params.get('tlang') || '').toLocaleLowerCase()

            if (!zhReg.test(lang) && !zhReg.test(tlang)) {
                let userLang
                try {
                    JSON.parse(ytplayer.config.args.player_response).captions.playerCaptionsTracklistRenderer.captionTracks.forEach(lang => {
                        lang.languageCode = lang.languageCode.toLocaleLowerCase()
                        if (userLang && userLang.languageCode == 'zh-cn') return
                        if (zhReg.test(lang.languageCode)) {
                            lang.baseUrl += '&fmt=srv3'
                            userLang = lang
                        }
                    })
                } catch (error) {
                    console.log(error)
                }

                let xhr = new XMLHttpRequest();
                xhr.open('GET', userLang ? userLang.baseUrl : `${url}&tlang=zh-Hans`, false);
                xhr.send();

                xhr.responseXML.querySelectorAll('p').forEach(e => {
                    let p = response.xml.querySelector(`p[t='${e.getAttribute('t')}']`);
                    if (p) {
                        if (p.childElementCount && e.previousElementSibling) {
                            let previous = e.previousElementSibling;
                            previous.setAttribute('d', e.getAttribute('t') - previous.getAttribute('t'));
                        }

                        e.textContent = [p.textContent.replace('\n', ' '), e.textContent.replace('\n', ' ')].join('\n');
                    }
                });

                response.text = new XMLSerializer().serializeToString(xhr.responseXML);
            }
        }
    });

})();