Userscript, which adds the ability to clear the users Watch Later queue on Youtube. Swedish interface only for now!

youtubewatchlaterclear.user.js

// ==UserScript==
// @name     Clear Youtube Watch Later
// @name:sv Rensa Youtube "Watch Later"
// @description    Adds the ability to clear the users Watch Later queue on Youtube
// @description:sv Lägger till förmogan att rensa "Watch Later" listan på Youtube
// @version  0.1
// @author Anders O.H Moberg
// @homepageURL https://a-moberg.com/
// @grant    none
// @match    https://www.youtube.com/playlist?list=WL*
// @updateURL https://gist.github.com/AndersMoberg/0a9f996a49d7b3a9e9c01065ce29abf4/raw/youtubewatchlaterclear.user.js
// @downloadURL https://gist.github.com/AndersMoberg/0a9f996a49d7b3a9e9c01065ce29abf4/raw/youtubewatchlaterclear.user.js
// ==/UserScript==

const selectorLocale = {
    'sv-SE': {
        button: 'Rensa lista',
        action: 'Åtgärdsmeny',
        remove: 'Ta bort från',
        userscriptConfirmation: 'Om du trycker OK, så börjar vi rensa.',
        userscriptStartupNotification: 'Videos börja rensas!',
        userscriptDoneNotification: 'Videos är klarrensade!',
    }
}

function awaitUntilCanFindButtonbar() {
    const buttonBarSelector = "ytd-menu-renderer.style-scope.ytd-playlist-header-renderer"

    return new Promise(resolve => {
        let intervalId;
        const monkey = function () {
            let buttonBar = document.querySelector(buttonBarSelector);
            console.log(buttonBar)
            if (buttonBar != undefined) {
                clearInterval(intervalId)
                resolve(buttonBar);
            }
        }

        intervalId = setInterval(monkey, 1000)
    })
}
let localeKey;
function setLocale() {
    localeKey = document.querySelector('html').getAttribute("lang")
}
function getLocaleObj() {
    return selectorLocale[localeKey];
}

window.addEventListener("load", async function () {
    setLocale();
    if (getLocaleObj() == undefined) {
        console.error("There is no support for " + locale);
        return;
    }

    let buttonBar = await awaitUntilCanFindButtonbar();
    let button = document.createElement("button");
    button.innerText = getLocaleObj().button;
    button.onclick = () => {
        if (window.confirm(getLocaleObj().userscriptConfirmation)) {
            clearVideoIntervalID = setInterval(clearVideo, msInterval);
            GM.notification(getLocaleObj().userscriptStartupNotification, "Youtube Watch Later");
        }
    }
    buttonBar.appendChild(button);
});

const msInterval = 750;
let clearVideoIntervalID;

function clearVideo() {
    meny = document.querySelector(`#primary button[aria-label="${getLocaleObj().action}"]`);
    if (meny === null) {
        clearInterval(clearVideoIntervalID);
        GM.notification(getLocaleObj().userscriptDoneNotification, "Youtube Watch Later");
    }

    meny.click();
    var things = document.evaluate(`//span[contains(text(),"${getLocaleObj().remove}")]`, document, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
    for (var i = 0; i < things.snapshotLength; i++) {
        things.snapshotItem(i).click();
    }
}

This is my first userscript, and my first one public to boot.
Thanks a lot to the people of this comment thread for references: https://gist.github.com/astamicu/eb351ce10451f1a51b71a1287d36880f