class MyDateTime extends \DateTime { public function format ($f) { $s = parent::format($f); $daynames = ['日', '月', '火', '水', '木', '金', '土']; $dayname = $daynames[parent::format('w')]; return str_replace('x', $dayname, $s); } } class MyDateTime extends \DateTime { const DAYNAME_SET = [ 'ja' => ['日', '月', '火', '水', '木', '金', '土'], 'ru' => ['вс', 'пн', 'вт', 'ср', 'чт', 'пт', 'сб'] ]; public function