function validLangs(langArray) {
  // account for our external API tests passing non-array things
  langArray = Array.isArray(langArray) ? langArray : langs;

  let codes = [];
  langArray.forEach((lang, index) => {
    const char = String.fromCharCode(index + 96).replace('`', '');
    if (Array.isArray(lang)) {
      codes = codes.concat(validLangs(lang).map(newLang => char + newLang));
    } else {
      codes.push(char);
    }
  });

  return codes;
}
Returns array of valid language codes
@deprecated
@method validLangs
@memberof axe.utils
@return {Array<string>} Valid language codes