code: public function shouldFallback($locale = null)
      {
          if (!$this->getWithFallback() || !$this->getFallbackLocale()) {
              return false;
          }
  
          $locale = $locale ?: $this->getLocale();
  
          return $locale != $this->getFallbackLocale();
      }
docs: Should fallback to a primary translation.
  
  @param string|null $locale
  @return bool