Кнопка-переключатель не работает

const switchers = document.querySelectorAll('.switcher');

const changeText = (switcher, lang) => {
  const texts = switcher.querySelectorAll('span');
  const sup = switcher.querySelector('sup');
  texts.forEach(text => {
    if (text.dataset.lang === lang) {
      text.classList.remove('hide');
      sup.innerText = text.dataset.lang;
      switcher.dataset.langSelected = lang;
    } else text.classList.add('hide');
  })
};

const switchLanguage = switcher => {
  const texts = switcher.querySelectorAll('span');
  const textsArray = Array.prototype.slice.call(texts);

  let lang = switcher.dataset.langSelected;

  if (lang !== null) {
    const textCount = texts.length;
    const selectedText = switcher.querySelector('span[data-lang="' + lang + '"]');
    const selectedIndex = textsArray.indexOf(selectedText);

    if (textCount - selectedIndex === 1) lang = textsArray[0].dataset.lang;
    else lang = textsArray[selectedIndex + 1].dataset.lang;
  }

  changeText(switcher, lang);
};

switchers.forEach(switcher => {
  changeText(switcher, switcher.dataset.langDefault);
  const sup = switcher.querySelector('sup');

  sup.addEventListener('click', () => {
    switchLanguage(switcher);
  });
});

.switcher span {
  font: 400 14px/18px Georgia, Palatino, 'Palatino Linotype', Times, 'Times New Roman', serif;
  color: #062636;
}

.switcher sup {
  background: #007fb2;
  color: #fff;
  border: 1px solid #007fb2;
  text-indent: 0;
  border-radius: 2px;
  vertical-align: middle;
  width: 15px;
  height: 15px;
  text-align: center;
  font: 400 8px/15px Arial, 'Helvetica Neue', Helvetica, sans-serif;
  cursor: pointer;
  display: inline-block;
  user-select: none;
}

.switcher sup:hover:before {
  content: '\21C4';
  width: 100%;
  height: 100%;
  font-size: 12px;
  font-weight: bold;
  display: block;
}

.switcher span.hide {
  display: none;
}

<div>
  <p>
  </p>
  <div class="switcher" data-lang-default="EN">
    <sup>EN</sup>
    <span data-lang="RU" class="hide"><font size="3"><em>Студент своевременно завершил проект.</em></font></span>
    <span data-lang="EN"><font size="3"><em>The student put his project across timely.</em></font></span>
    <p></p>
  </div>