modified.user.js

// ==UserScript==
// @name        WWT [worldwidetorrents.eu] - Subtitle download links to TV and Movie torrents
// @description Adds download links for subtitles to every TV and movie torrent on WWT (addic7ed & subscene)
// @namespace   NotNeo
// @include     http*://worldwidetorrents.eu/torrents-details.php*
// @require     https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js
// @version     1.0.1
// @grant       none
// ==/UserScript==

$(document).ready(() => {
    const btnBar = $(".glyphicon.glyphicon-download").parent().parent().parent();
    const cat = $(".category_id_bar").text();
    const torrentTitle = $(".fltRight").prev().prev().text();
    let baseURL;

    if (/^TV.*/ig.test(cat)) {
        baseURL = "http://www.addic7ed.com/search.php?search=";
    } else if (/^Movies.*/ig.test(cat)) {
        baseURL = "https://subscene.com/subtitles/title?q=";
    }

    btnBar.append(`<a href="${baseURL}${encodeURI(torrentTitle)}" target="_blank" class="btn btn-default"><span class="fa fa-fw fa-comment"></span> Download Subtitles</a>`);
});

Changelog:

• Removed duplicated code (mostly selector definition)
• Removed code for changing to + and removing spaces
• Not entirely sure of the purpose of the for loops. Removed them as it is unrequired (changed to regex and encodeURI())