enableTrackButton (track) {
    const
      t = this,
      lang = track.srclang,
      target = document.getElementById(`${track.trackId}-btn`)
    ;
    if (!target) {
      return;
    }

    let label = track.label;

    if (label === '') {
      label = i18n.t(mejs.language.codes[lang]) || lang;
    }
    target.disabled = false;
    const targetSiblings = siblings(target, (el) => hasClass(el, `${t.options.classPrefix}captions-selector-label`));
    for (let i = 0; i < targetSiblings.length; i++) {
      targetSiblings[i].innerHTML = label;
    }
  }
Enable the input for the caption/subtitle and remove the "loading" notification from the label.
@param {object} track