function _localizeIcuMessage(icuMessage, locale) {
  const localeMessages = _getLocaleMessages(locale);
  const localeMessage = localeMessages[icuMessage.i18nId];

  // Use the DEFAULT_LOCALE fallback (usually the original english message) if we couldn't
  // find a message in the specified locale. Possible reasons:
  //  - string drift between Lighthouse versions
  //  - in a bundle stripped of locale files but running in the DEFAULT_LOCALE
  //  - new strings haven't been updated yet in a local dev run
  // Better to have an english message than no message at all; in some cases it
  // won't even matter.
  if (!localeMessage) {
    return icuMessage.formattedDefault;
  }

  return formatMessage(localeMessage.message, icuMessage.values, locale);
}
Retrieves the localized version of `icuMessage` and formats with any given
value replacements.
@param {LH.IcuMessage} icuMessage
@param {LH.Locale} locale
@return {string}