JSFiddle - React, Tailwind, and code Playground

HTML

<p class="input">
  <b>Entrée : </b>
  <span></span>
</p>
<p class="output">
  <b>Entrée : </b>
  <span></span>
</p>

JavaScript

var textWithoutSpecialChars = "Je suis un nain, tu es un nain, elle est une naine",
	excluded_words = 'je,tu,il,elle,nous,vous,ils,elles',
  regex;
  
function replacer(word) {
	regex = new RegExp(word, "gi");
  textWithoutSpecialChars = textWithoutSpecialChars.replace(word, '');
};

excluded_words = excluded_words.split(','); // Tu convertis ta String en Array
console.log(excluded_words);;

document.querySelector('.input > span').innerText = textWithoutSpecialChars;

excluded_words.forEach(function (word) {
    replacer(word.toLowerCase()); // Recherche du mot en lowcase
    replacer(word.toUpperCase()); // Recherche du mot en upcase
    var capitalizedWord = word.charAt(0).toUpperCase() + word.slice(1,word.length);
    replacer(capitalizedWord); // Recherche du mot "capitalisé"
});
console.log(textWithoutSpecialChars);

document.querySelector('.output > span').innerText = textWithoutSpecialChars;