protected static function getPattern($currency)
    {
        if (!$currency) {
            return '{{ widget }}';
        }

        $locale = \Locale::getDefault();

        if (!isset(self::$patterns[$locale])) {
            self::$patterns[$locale] = [];
        }

        if (!isset(self::$patterns[$locale][$currency])) {
            $format = new \NumberFormatter($locale, \NumberFormatter::CURRENCY);
            $pattern = $format->formatCurrency('123', $currency);

            // the spacings between currency symbol and number are ignored, because
            // a single space leads to better readability in combination with input
            // fields

            // the regex also considers non-break spaces (0xC2 or 0xA0 in UTF-8)

            preg_match('/^([^\s\xc2\xa0]*)[\s\xc2\xa0]*123(?:[,.]0+)?[\s\xc2\xa0]*([^\s\xc2\xa0]*)$/u', $pattern, $matches);

            if (!empty($matches[1])) {
                self::$patterns[$locale][$currency] = $matches[1].' {{ widget }}';
            } elseif (!empty($matches[2])) {
                self::$patterns[$locale][$currency] = '{{ widget }} '.$matches[2];
            } else {
                self::$patterns[$locale][$currency] = '{{ widget }}';
            }
        }

        return self::$patterns[$locale][$currency];
    }