That is not UTF-8, that is percent encoding also known as url encoding.

You can use decodeURIComponent() to convert it back before displaying it

$("#quote1 span").html(decodeURIComponent(text1));

Every obfuscated script needs some kind of eval. In here, the lines

_L = 'constr\x75\x63\x74\x6F\x72';
[][_L]_L)();

are doing this. _L is the string "constructor", and [].constructor.constructor is the Function constructor. It will be called with the decoded script, and the resulting function will be called. We can substitute it with an alert, paste the script in the console*, and wait for the result - we don't even need to understand how the decoding works. In your case, the result is (yes, including all the comments and linebreaks):

var alarm ="0";
var content = document;

if ((content.getElementById("wrapper") != null))
{
    document.getElementById('wrapper').style.display = 'block';
}

function a ()
{
    if ((content.getElementById("links") != null))
    {
        var temp = content.getElementById("links").innerHTML;
        if ((temp.indexOf('nofollow')+1) > 0)  alarm = "1";
        else if ((temp.indexOf('noindex')+1) > 0)  alarm = "1";
    }
    else alarm = "1";
}

function b ()
{
    if ((content.getElementById("aa") != null) && (content.getElementById("ab") != null))
    {
        temp = document.getElementById("aa").href;
        if ("http://uc-portaller.ru/" != temp) alarm = "1";

        temp = document.getElementById("ab").innerHTML;
        if ("скрипты для ucoz" != temp) alarm = "1";
    }
    else alarm = "1";
}

function c ()
{
    if ((content.getElementById("ba") != null) && (content.getElementById("bb") != null))
    {

        temp = content.getElementById("ba").href;
        if ("http://austere.ru/" != temp) alarm = "1";

        temp = content.getElementById("bb").innerHTML;
        if ("доска объявлений" != temp) alarm = "1";
    }
    else alarm = "1";
}

function d ()
{
    if ((content.getElementById("ca") != null) && (content.getElementById("cb") != null))
    {

        temp = content.getElementById("ca").href;
        if ("http://www.for-creative.com/" != temp) alarm = "1";

        temp = content.getElementById("cb").innerHTML;
        if ("темы для ucoz" != temp) alarm = "1";
    }
    else alarm = "1";
}

a ();

if (alarm == "0") b ();
if (alarm == "0") c ();
if (alarm == "0") d ();

if (alarm == "1") prompt('Нарушены условия использования, по всем вопросам обращайтесь в ICQ:', '376880395');












$(document).ready(function(){

    //When you click on a link with class of poplight and the href starts with a # 
    $('a.poplight[href^=#]').click(function() {
        var popID = $(this).attr('rel'); //Get Popup Name
        var popURL = $(this).attr('href'); //Get Popup href to define size

        //Pull Query & Variables from href URL
        var query= popURL.split('?');
        var dim= query[1].split('&');
        var popWidth = dim[0].split('=')[1]; //Gets the first query string value

        //Fade in the Popup and add close button
        $('#' + popID).fadeIn().css({ 'width': Number( popWidth ) }).prepend('');

        //Define margin for center alignment (vertical + horizontal) - we add 80 to the height/width to accomodate for the padding + border width defined in the css
        var popMargTop = ($('#' + popID).height() + 80) / 2;
        var popMargLeft = ($('#' + popID).width() + 80) / 2;

        //Apply Margin to Popup
        $('#' + popID).css({ 
            'margin-top' : -popMargTop,
            'margin-left' : -popMargLeft
        });

        //Fade in Background
        $('body').append('<div id="fade"></div>'); //Add the fade layer to bottom of the body tag.
        $('#fade').css({'filter' : 'alpha(opacity=0)'}).fadeIn(); //Fade in the fade layer 

        return false;
    });


    //Close Popups and Fade Layer
    $('a.close, #fade').live('click', function() { //When clicking on the close or fade layer...
        $('#fade , .popup_block').fadeOut(function() {
            $('#fade, a.close').remove();  
    }); //fade them both out

        return false;
    });


});




        $.fn.tabs = function () {
            return this.each(function () {
               var $tabwrapper = $(this); 

               var $panels = $tabwrapper.find('> div');
               var $tabs = $tabwrapper.find('> ul a');

               $tabs.click(function () {  
                   $tabs.removeClass('selected');
                   $(this).addClass('selected');

                   $panels
                    .hide() // hide ALL the panels
                    .filter(this.hash) // filter down to 'this.hash'
                        .show(); // show only this one

                   return false;
               }).filter(window.location.hash ? '[hash=' + window.location.hash + ']' : ':first').click();
            });
        };

        $(document).ready(function () {
            // console.log(window.location.hash);

            $('div.tabs').tabs();
        });

*) Of course you need to be sure what you're doing. There's always a small risk that it's a malicious script, and you might have not found all evals. @jfriend00's tip on executing the decoding snippets line-by-line is a safer way.