function equal(bundles1, bundles2) {
  return bundles1.length === bundles2.length &&
    bundles1.every(({lang}, i) => lang === bundles2[i].lang);
}
Test if two fallback chains are functionally the same.

@param   {Array<ResourceBundle>} bundles1
@param   {Array<ResourceBundle>} bundles2
@returns {boolean}
@private