Remove the regular space that you have first in the pattern:

 str = str.replace(/[\u00A0\u1680​\u180e\u2000-\u2009\u200a​\u200b​\u202f\u205f​\u3000]/g,'');

@adeneo posted an option using jQuery. Here's a relevant answer I found that doesn't use jQuery. From this answer: What's the right way to decode a string that has special HTML entities in it?

function parseHtmlEnteties(str) {
    return str.replace(/&#([0-9]{1,4});/gi, function(match, numStr) {
        var num = parseInt(numStr, 10); // read num as normal number
        return String.fromCharCode(num);
    });
}

By using Regx. in string replace you can achieve this. See the below code

var unicode_dictionary = {
    "\\00E9": "é",
    "\\00E0": "à"
}


var old_str = "rapport couvrant une p\00E9riode de 6 mois (f\00E9vrier \00E0 juillet)"

function convert(){
  for(var key in unicode_dictionary){    
      var regx=new RegExp(key,'g')
      old_str=old_str.replace(regx,unicode_dictionary[key]);
   }
  alert(old_str);
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<button onclick='convert()'>Convert</button>

Adapted from Semplice, following link from here.

[^\x00-\x80] matches any character not in the ASCII range.
Note that some of the characters may not be encoded correctly from the copy and paste.

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function embolden( str, chr ){
    return str.replace( /[^\x00-\x80]/g,
        function (a) { 
            return chr == latin_map[a] ? '<b>' + a + '</b>' : a;
        } 
    );
}

embolden( 'ádám', 'a' );    // "<b>á</b>d<b>á</b>m"

Sure is!

Running this in the Firebug console

"®ü".replace(/[®ü]/g,"replaced")

returned

"replacedreplaced"

You can also do

"®ü".replace(/[\xAE\xFC]/g,"Wohoo! ");

which returns

"Wohoo! Wohoo! "

A good hex symbol lookup page can be found at http://www.ascii.cl/htmlcodes.htm

Example

running this jQuery on this page

$(".post-text").text().replace(/®/g," ******** ")

returns

" is it possible to translate special characters like ******** , ü etc with javascript 
String replace function? Use this syntax... string.replace(/\xCC/g/,''); Where 'CC' is 
the hex character code for the char you are wanting to replace. In this example I am 
replacing with empty string ''. yes, and is as simple as can be: ' ******** '.replace('
 ******** ','anything'); Sure is! Running this in the Firebug console " ******** ü".
replace(/[ ******** ü]/g,"replaced") returned replacedreplaced "

RegEx Improvements

The regex can be shortened by using case-insensitive match with i flag. We can remove the characters which are added as both lowercase and uppercase in the regex.

After removing lowercase characters regex will be as below

\?ÕÌ_|Š|Ž|À|Á|Â|Ã|Ä|Å|Æ|Ç|È|É|Ê|Ë|Ì|Í|Î|Ï|Ñ|Ò|Ó|Ô|Õ|Ö|Ø|Ù|Ú|Û|Ü|Ý|Þ|ß|ð|ÿ|_Œ‚|__|_

Here's live demo of regex

The regex can be further improved by using character class which will make the matches faster than OR conditions

\?ÕÌ_|_Œ‚|[ŠŽÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÑÒÓÔÕÖØÙÚÛÜÝÞßðÿ_]+

Adding + quantifier also has positive effect on the number of steps taken to match characters when the characters in the character class are consecutive/adjacent to each other.

Here's the demo on RegEx101, without + quantifier^Screenshot and with + quantifier^screenshot applied on the same data. Note that in these demos, PHP is selected as the steps taken to match is not shown for JavaScript. Also, the regex is different, it also contains lowercase counterparts of those special characters as i flag is not working with PHP and don't want to apply u(Unicode) flag as it is not supported in JavaScript.

These demos are created only to show difference when + is applied on character class. The effect should be similar in JavaScript.

Note that the __(two underscores) are redundant as _ is already added in character class and with g flag it'll remove all occurrences.

Method Chaining

As replace returns a string, any other string method can be called on it. Multiple calls to replace can be chained.

str.replace(someRegexOrString, someString)
    .replace(someOtherRegexOrString, someOtherString);

This is equivalent to

var temp = str.replace(someRegexOrString, someString);
var result = temp.replace(someOtherRegexOrString, someOtherString);

Replacing HTML

jQuery html() accepts a function which will receive the current innerHTML of the element on which the method is called as parameter and replaces the returned content to the element.

The code can be written as

$('.rte').html(function(index, currentHTML) {
    return doSomeOperationOn(currentHTML);
});

Complete Code

With above changes, the code will be

$(document).ready(function() {
    var regex = /\?ÕÌ_|_Œ‚|[ŠŽÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÑÒÓÔÕÖØÙÚÛÜÝÞßðÿ_]+/gi;

    $('.rte').html(function(i, oldHTML) {
        return oldHTML.replace(regex, ' ')
            .replace(/[^\x00-\x7F]|\?/g, '');
    });
});

$(document).ready(function() { is more readable than $(function() {. So, you may also consider using more expressive form.

HTML entities get converted to actual unicode characters. Example:

document.body.innerHTML = "⇈";


console.log(document.body.innerHTML === "\u21c8"); // true

// Instead of a unicode esape sequence, you can write the
// actual unicode character. This is safe as long as you
// specify the correct encoding for your JavaScript files:
console.log(document.body.innerHTML === "⇈"); // true
	

So when you read the innerHTML via $(this).html() or the textContent via $(this).text(), you need to look for the actual unicode character given by its unicode escape sequence "\u21c8" or directly "⇈" and not its entity "⇈".