<form action='http://site.ru/testpost.php' method='POST'>
<select name='test[xx]'>
<option value='1'>1
<option value='2'>2
</select>
<select name='test[yy]'>
<option value='1'>1
<option value='2'>2
</select>
<input type='submit'>
</form><?php
print_r($_POST);
?>Array ( [test] => Array ( [xx] => 1 [yy] => 1 ) )
$language = 'english';
$stmt = $pdo->query("SELECT `key`, `{$language}` AS `translation` FROM `language`");
$translation = [];
while ($item = $stmt->fetch(PDO::FETCH_ASSOC)) {
$translation[$item['key']] = $item['translation'];
}