Steam Broadcast Chat Cleaner - cleans up the chat of any Steam Broadcast, massively increasing the conversation quality. Works on Dota 2's Watch page as well. Requires Greasemonkey (Firefox) or Tampermonkey (Chrome). Screenshots: http://i.imgur.com/7qEfM9B.png, http://i.imgur.com/PHW4TbK.png - Click "Raw" to install.

SteamBroadcastChatCleaner.user.js

// ==UserScript==
// @name         Steam Broadcast Chat Cleaner
// @namespace    http://jzhang.net/
// @version      3.1.1
// @description  Cleans up Steam Broadcast chat
// @author       waylaidwanderer
// @include      http://steamcommunity.com/broadcast/watch/*
// @require      //code.jquery.com/jquery-1.11.3.min.js
// @downloadURL  https://gist.github.com/waylaidwanderer/6bb095e0731ef41d49dc/raw/SteamBroadcastChatCleaner.user.js
// @updateURL    https://gist.github.com/waylaidwanderer/6bb095e0731ef41d49dc/raw/SteamBroadcastChatCleaner.user.js
// @grant        GM_getValue
// @grant        GM_setValue
// @grant        GM_addStyle
// ==/UserScript==

(function(){
    function GM_wait()
    {
        if (typeof jQuery != 'undefined') {
            letsJQuery(jQuery);
        } else if (typeof unsafeWindow.jQuery == 'undefined') {
            window.setTimeout(GM_wait,100);
        }
        else {
            unsafeWindow.jQuery(function() { letsJQuery(unsafeWindow.jQuery); });
        }
    }
    GM_wait();

    function letsJQuery($)
    {
        var $body = $('body');

        var englishOnly = GM_getValue("englishOnly", false);
        var noEmoticonsOnly = GM_getValue("noEmoticonsOnly", true);
        var noEmoticonsOnlyPercent = GM_getValue("noEmoticonsOnlyPercent", 50);
        var noAllCaps = GM_getValue("noAllCaps", true);
        var noAllCapsPercent = GM_getValue("noAllCapsPercent", 80);
        var noRepeatedText = GM_getValue("noRepeatedText", true);
        var noRepeatedTextMaxRepeats = GM_getValue("noRepeatedTextMaxRepeats", 2);
        var noShortMessages = GM_getValue("noShortMessages", true);
        var noShortMessagesMinLength = GM_getValue("noShortMessagesMinLength", 3);
        var noRepeatedMessages = GM_getValue("noRepeatedMessages", true);
        var noRepeatedMessagesMaxRepeats = GM_getValue("noRepeatedMessagesMaxRepeats", 1);
        var noRepeatedMessagesMuteUser = GM_getValue("noRepeatedMessagesMuteUser", false);
        var showMessageRemoved = GM_getValue("showMessageRemoved", false);
        var enableWordFilter = GM_getValue("enableWordFilter", false);
        var wordFilter = GM_getValue("wordFilter", "").split(",");

        $(".EmoticonContainer").after("<div class=\"EmoticonContainer ChatSettings\" style=\"cursor: pointer;\"><span style=\"opacity: 0.4; display: inline-block; height: 22px; width: 22px; margin-top: 4px; vertical-align: middle; background: url('data:image/png;base64,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') no-repeat center;\">&nbsp;</span></div>");

        var settingsClass = (window.location != window.parent.location) ? "iframe" : "no-iframe";
        $body.append ('\
            <div id="chat-settings" class="'+settingsClass+'">\
                <form>\
                    <div class="form-group">\
                        <input type="checkbox" id="englishOnly"'+(englishOnly ? " checked" : "")+'>\
                        <label for="englishOnly">Hide Non-English Messages (also hides emoticons which use Unicode characters like <span style=\"display: inline-block;\">( ͡° ͜ʖ ͡°))</span></label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noEmoticonsOnly"'+(noEmoticonsOnly ? " checked" : "")+'>\
                        <label for="noEmoticonsOnly">Hide Emoticons-Only Messages</label>\
                        <br>\
                        <input type="number" id="noEmoticonsOnlyPercent" min="0" max="100" style="margin: 5px auto 5px 25px;" value="'+noEmoticonsOnlyPercent+'">\
                        <label for="noEmoticonsOnlyPercent">% of message that has to be emoticons (emoticons count as 1.5 characters)</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noAllCaps"'+(noAllCaps ? " checked" : "")+'>\
                        <label for="noAllCaps">Hide ALL-CAPS Messages</label>\
                        <br>\
                        <input type="number" id="noAllCapsPercent" min="0" max="100" style="margin: 5px auto 5px 25px;" value="'+noAllCapsPercent+'">\
                        <label for="noAllCapsPercent">% of message that has to be ALL CAPS</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noRepeatedText"'+(noRepeatedText ? " checked" : "")+'>\
                        <label for="noRepeatedText">Hide Repeated-Characters/Words Messages</label>\
                        <br>\
                        <input type="number" id="noRepeatedTextMaxRepeats" min="1" style="margin: 5px auto 5px 25px;" value="'+noRepeatedTextMaxRepeats+'">\
                        <label for="noRepeatedTextMaxRepeats">Maximum # of repeated occurrences</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noShortMessages"'+(noShortMessages ? " checked" : "")+'>\
                        <label for="noShortMessages">Hide Short Messages</label>\
                        <br>\
                        <input type="number" id="noShortMessagesMinLength" min="0" style="margin: 5px auto 5px 25px;" value="'+noShortMessagesMinLength+'">\
                        <label for="noShortMessagesMinLength">Minimum # of characters</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="noRepeatedMessages"'+(noRepeatedMessages ? " checked" : "")+'>\
                        <label for="noRepeatedMessages">Hide Repeated Messages</label>\
                        <br>\
                        <input type="number" id="noRepeatedMessagesMaxRepeats" min="0" style="margin: 5px auto 5px 25px;" value="'+noRepeatedMessagesMaxRepeats+'">\
                        <label for="noRepeatedMessagesMaxRepeats"># of repeated messages before action</label>\
                        <br>\
                        <input type="checkbox" id="noRepeatedMessagesMuteUser" style="margin: 5px auto 5px 25px;"'+(noRepeatedMessagesMuteUser ? " checked" : "")+'>\
                        <label for="noRepeatedMessagesMuteUser">Also mute user</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="enableWordFilter"'+(enableWordFilter ? " checked" : "")+'>\
                        <label for="enableWordFilter">Enable word filter</label>\
                        <br>\
                        <input type="text" id="wordFilter" style="margin: 5px auto 5px 25px;" value="'+wordFilter+'">\
                        <label for="wordFilter">Comma-delimited list of words to filter (case insensitive). Prepend word with * for case-sensitive word (e.g. "*LoL")</label>\
                    </div>\
                    <div class="form-group">\
                        <input type="checkbox" id="showMessageRemoved"'+(showMessageRemoved ? " checked" : "")+'>\
                        <label for="showMessageRemoved">Show "&lt;message deleted&gt;" instead of hiding message</label>\
                    </div>\
                    <div class="buttons">\
                        <a href="#" class="close ChatSend">Close</a>\
                        <a href="#" class="save ChatSend">Save</a>\
                    </div>\
                </form>\
            </div>\
        ');

        $body.on('mouseenter', '.ChatSettings span', function() {
            $(this).css('opacity', 1);
        });

        $body.on('mouseleave', '.ChatSettings span', function() {
            $(this).css('opacity', 0.4);
        });

        $body.on('click', '#chat-settings .close', function() {
            $("#chat-settings").hide();
        });

        $body.on('click', '#chat-settings .save', function() {
            GM_setValue("englishOnly", $("#englishOnly").is(':checked'));
            GM_setValue("noEmoticonsOnly", $("#noEmoticonsOnly").is(':checked'));
            GM_setValue("noEmoticonsOnlyPercent", $("#noEmoticonsOnlyPercent").val());
            GM_setValue("noAllCaps", $("#noAllCaps").is(':checked'));
            GM_setValue("noAllCapsPercent", $("#noAllCapsPercent").val());
            GM_setValue("noRepeatedText", $("#noRepeatedText").is(':checked'));
            GM_setValue("noRepeatedTextMaxRepeats", $("#noRepeatedTextMaxRepeats").val());
            GM_setValue("noShortMessages", $("#noShortMessages").is(':checked'));
            GM_setValue("noShortMessagesMinLength", $("#noShortMessagesMinLength").val());
            GM_setValue("noRepeatedMessages", $("#noRepeatedMessages").is(':checked'));
            GM_setValue("noRepeatedMessagesMaxRepeats", $("#noRepeatedMessagesMaxRepeats").val());
            GM_setValue("noRepeatedMessagesMuteUser", $("#noRepeatedMessagesMuteUser").is(':checked'));
            GM_setValue("showMessageRemoved", $("#showMessageRemoved").is(':checked'));
            GM_setValue("enableWordFilter", $("#enableWordFilter").is(':checked'));
            GM_setValue("wordFilter", $("#wordFilter").val());
            englishOnly = GM_getValue("englishOnly", true);
            noEmoticonsOnly = GM_getValue("noEmoticonsOnly", true);
            noEmoticonsOnlyPercent = GM_getValue("noEmoticonsOnlyPercent", true);
            noAllCaps = GM_getValue("noAllCaps", true);
            noAllCapsPercent = GM_getValue("noAllCapsPercent", 80);
            noRepeatedText = GM_getValue("noRepeatedText", true);
            noRepeatedTextMaxRepeats = GM_getValue("noRepeatedTextMaxRepeats", 2);
            noShortMessages = GM_getValue("noShortMessages", true);
            noShortMessagesMinLength = GM_getValue("noShortMessagesMinLength", 3);
            noRepeatedMessages = GM_getValue("noRepeatedMessages", true);
            noRepeatedMessagesMaxRepeats = GM_getValue("noRepeatedMessagesMaxRepeats", 2);
            noRepeatedMessagesMuteUser = GM_getValue("noRepeatedMessagesMuteUser", false);
            showMessageRemoved = GM_getValue("showMessageRemoved", false);
            enableWordFilter = GM_getValue("enableWordFilter", false);
            wordFilter = GM_getValue("wordFilter", "").split(",");
            $("#chat-settings").hide();
        });

        $body.on('click', '.ChatSettings', function() {
            $("#chat-settings").toggle();
        });

        $body.on('click', '.message-removed a', function() {
            $(this).hide();
            $(this).parent().find('span').show();
        });

        waitForKeyElements("#ChatMessages div.ChatMessage", processMessages);
        var repeatedMessages = [];

        function processMessages(jNode) {
            var remove = false;
            var message = jNode.find(".tmplChatMessage").text();

            var originalMessage = jNode.find(".tmplChatMessage").html();
            message = message.replace(/<img[^>]*>/g,"").trim();

            if (noEmoticonsOnly && !remove) {
                if (message == "") {
                    remove = true;
                } else {
                    var div = "<div>" + originalMessage + "</div>";
                    var numEmoticons = $(div).find('img').length;
                    if (parseFloat(numEmoticons * 1.5 / (message.length + numEmoticons) * 100) >= noEmoticonsOnlyPercent) {
                        remove = true;
                    }
                }
            }
            if (englishOnly && !remove) {
                var regex = /[^\x00-\x7F]+/;
                if (message.match(regex)) {
                    remove = true;
                }
            }
            if (noShortMessages && !remove) {
                if (message.length < noShortMessagesMinLength) {
                    remove = true;
                }
            }
            if (noAllCaps && !remove) {
                var numCaps = 0;
                var tmpMessage = message.replace(/\s+/g, '');
                for (var i = 0; i < tmpMessage.length; i++) {
                    var char = tmpMessage[i];
                    if (char == char.toUpperCase()) {
                        numCaps++;
                    }
                }
                if (parseFloat(numCaps / tmpMessage.length * 100) >= noAllCapsPercent) {
                    remove = true;
                }
            }
            if (noRepeatedText && !remove) {
                var tmpMessage = message.replace(/\s+/g, '').toLowerCase();

                var repeats = [];
                var lengthToCheck = 1;
                while (lengthToCheck < tmpMessage.length) {
                    var chunks = chunkString(tmpMessage, lengthToCheck);
                    for (var i = 0; i < chunks.length; i++) {
                        var nextChunk = (typeof chunks[i+1] === 'undefined') ? "" : chunks[i+1];
                        if (chunks[i] == nextChunk) {
                            var foundRepeat = false;
                            for (var j = 0; j < repeats.length; j++) {
                                var repeatData = repeats[j];
                                if (repeatData.value == chunks[i]) {
                                    repeatData.numRepeats++;
                                    foundRepeat = true;
                                    if (repeatData.numRepeats > noRepeatedTextMaxRepeats) {
                                        remove = true;
                                    }
                                    break;
                                }
                            }
                            if (remove) {
                                break;
                            } else if (!foundRepeat) {
                                var data = {
                                    value: chunks[i],
                                    numRepeats: 1
                                };
                                repeats.push(data);
                            }
                        }
                    }
                    lengthToCheck++;
                }
            }
            if (noRepeatedMessages && !remove) {
                var steamId = jNode.attr("data-steamid");
                var found = false;
                for (var i = 0; i < repeatedMessages.length; i++) {
                    var user = repeatedMessages[i];
                    if (!user.muted) {
                        if (user.steamId == steamId) {
                            found = true;
                            if (user.lastMessage == message) {
                                user.numRepeats++;
                                if (user.numRepeats > noRepeatedMessagesMaxRepeats) {
                                    if (noRepeatedMessagesMuteUser) {
                                        user.muted = true;
                                        var personaName = jNode.find(".tmplChatName").text();
                                        BroadcastWatch.GetChat().MuteUser(steamId, personaName);
                                    }
                                    remove = true;
                                }
                            } else {
                                user.lastMessage = message;
                            }
                            break;
                        }
                    }
                }
                if (!found) {
                    var data = {
                        steamId: steamId,
                        lastMessage: message,
                        numRepeats: 0,
                        muted: false
                    };
                    repeatedMessages.push(data);
                }
            }
            if (enableWordFilter && !remove) {
                var words = message.replace(/[.,-\/#!$%\^&\*;:{}=\-_`~()]/g,'').split(" ");
                for (var i = 0; i < words.length; i++) {
                    var word = words[i].trim();
                    if (word != "") {
                        for (var j = 0; j < wordFilter.length; j++) {
                            var filterWord = wordFilter[j].trim();
                            var caseSensitive = filterWord.charAt(0) == "*";
                            if (caseSensitive) {
                                filterWord = filterWord.replace("*", "");
                                if (filterWord == word) {
                                    remove = true;
                                    break;
                                }
                            } else {
                                if (filterWord.toLowerCase() == word.toLowerCase()) {
                                    remove = true;
                                    break;
                                }
                            }
                        }
                        if (remove) {
                            break;
                        }
                    }
                }
            }

            if (remove) {
                if (showMessageRemoved) {
                    jNode.find(".tmplChatMessage").html("<span class=\"message-removed\"><a href=\"#\">&lt;message deleted&gt;</a><span style=\"display: none;\">"+originalMessage+"</span></span>");
                } else {
                    var chat = BroadcastWatch.GetChat();
                    jNode.remove();
                    chat.TrimChat();
                    chat.UpdateScroll();
                }
            }
        }

        function chunkString(str, length) {
            return str.match(new RegExp('.{1,' + length + '}', 'g'));
        }

        function waitForKeyElements (
            selectorTxt,    /* Required: The jQuery selector string that
             specifies the desired element(s).
             */
            actionFunction, /* Required: The code to run when elements are
             found. It is passed a jNode to the matched
             element.
             */
            bWaitOnce,      /* Optional: If false, will continue to scan for
             new elements even after the first match is
             found.
             */
            iframeSelector  /* Optional: If set, identifies the iframe to
             search.
             */
        ) {
            var targetNodes, btargetsFound;

            if (typeof iframeSelector == "undefined")
                targetNodes     = $(selectorTxt);
            else
                targetNodes     = $(iframeSelector).contents ()
                    .find (selectorTxt);

            if (targetNodes  &&  targetNodes.length > 0) {
                btargetsFound   = true;
                /*--- Found target node(s).  Go through each and act if they
                 are new.
                 */
                targetNodes.each ( function () {
                    var jThis        = $(this);
                    var alreadyFound = jThis.data ('alreadyFound')  ||  false;

                    if (!alreadyFound) {
                        //--- Call the payload function.
                        var cancelFound     = actionFunction (jThis);
                        if (cancelFound)
                            btargetsFound   = false;
                        else
                            jThis.data ('alreadyFound', true);
                    }
                } );
            }
            else {
                btargetsFound   = false;
            }

            //--- Get the timer-control variable for this selector.
            var controlObj      = waitForKeyElements.controlObj  ||  {};
            var controlKey      = selectorTxt.replace (/[^\w]/g, "_");
            var timeControl     = controlObj [controlKey];

            //--- Now set or clear the timer as appropriate.
            if (btargetsFound  &&  bWaitOnce  &&  timeControl) {
                //--- The only condition where we need to clear the timer.
                clearInterval (timeControl);
                delete controlObj [controlKey]
            }
            else {
                //--- Set a timer, if needed.
                if ( ! timeControl) {
                    timeControl = setInterval ( function () {
                            waitForKeyElements (    selectorTxt,
                                actionFunction,
                                bWaitOnce,
                                iframeSelector
                            );
                        },
                        0
                    );
                    controlObj [controlKey] = timeControl;
                }
            }
            waitForKeyElements.controlObj   = controlObj;
        }

        GM_addStyle("\
            #chat-settings {\
                display: none;\
                border: 3px double black;\
                z-index: 777;\
                border: 1px solid #4c4c4c;\
                background-color: #292929;\
            }\
            #chat-settings.no-iframe {\
                height: 492px;\
                width: 476px;\
                position: fixed;\
                top: 50%;\
                left: 50%;\
                margin-left:-238px;\
                margin-top:-273px;\
                padding: 2em;\
            }\
            #chat-settings.iframe {\
                height: 100%;\
                position: absolute;\
                padding: 1em;\
                top: 0;\
                bottom: 0;\
                left: 0;\
                right: 0;\
            }\
            #chat-settings .form-group {\
                padding-bottom: 5px;\
            }\
            #chat-settings input[type=number] {\
                width: 45px;\
            }\
            #chat-settings .buttons {\
                padding-top: 20px;\
            }\
            #chat-settings .ChatSend {\
                padding: 5px;\
            }\
        " );
    }
})();

Really nice user script. Concise and on the point the function for detection of repeated message often filters long messages with many the, due to the normal repetitions in english. Maybe filtering for regex should have an option for single character repetition and one for longer for 2 or 3 character regex. Otherwise any sentence of more than 14 characters most likely will get filtered.( eg: get filtered has 3 e and fails to normal settings).

Thanks @ProMPT120, I updated the script to fix it by removing regex and using my own custom code instead.

Still working for future TI6 broadcasts!