code: public function create(string $locale = null, string $currency = null)
      {
          $locale = $locale ?? $this->localeProvider->getCurrentLocale();
          $currency = $currency ?? $this->currencyProvider->getCurrentCurrency();
  
          if (isset($this->cache[$key = strtolower("$locale-$currency")])) {
              return $this->cache[$key];
          }
  
          return $this->cache[$key] = new Formatter($locale, $currency);
      }
docs: Creates a new formatter.
  
  @param string|null $locale
  @param string|null $currency
  
  @return Formatter