Letter post list

letter-post-list.php

<?php

$posts = get_posts([
	'post_status'		=> 'publish',
	'posts_per_page'	=> -1,
	'post_type' 		=> 'post'
]);
$post_index = array_fill_keys( array_merge( [ '#' ], range( 'a', 'z' ), ['å', 'ä', 'ö', ] ), [] );
foreach( $posts as $post ) {
	$first_letter = strtolower( substr( $post->post_title, 0, 1 ) );
	if( is_numeric( $first_letter ) ) {
		$post_index[ '#' ][] = $post;
	} else {
		$post_index[ $first_letter ][] = $post;
	}
}

$curent_letter = '';
echo '<ol>';
foreach( $post_index as $letter => $letter_list ) {
	echo '<li>' . $letter . '</li>';
	echo '<ol>';
	foreach( $letter_list as $post ) {
		echo '<li>' . $post->post_title . '</li>';
	}
	echo '</ol>';
}
echo '</ol>';