protected function formatLongYear(): string
    {
        if ($this->year < 0) {
            return /*  I18N: BCE=Before the Common Era, for Julian years < 0. See http://en.wikipedia.org/wiki/Common_Era */
                I18N::translate('%s&nbsp;BCE', I18N::digits(-$this->year));
        }

        if ($this->new_old_style) {
            return I18N::translate('%s&nbsp;CE', I18N::digits(sprintf('%d/%02d', $this->year - 1, $this->year % 100)));
        }

        /* I18N: CE=Common Era, for Julian years > 0. See http://en.wikipedia.org/wiki/Common_Era */
        return I18N::translate('%s&nbsp;CE', I18N::digits($this->year));
    }