<?php

$strs = [
	'/' => true,
	'/?foo=bar' => true,
	'/?' => true,
	'/en' => true,
	'/ru' => true,
	'/ru/foo' => false
];

$expr = '/^\/(en|ru)?(\?.*)?$/';

$success = true;
foreach ($strs as $str=>$expected) {
	$success = $success && $expected == preg_match($expr, $str);
}

echo $success ? 
   'Tests passed!' : 'Tests failed!';