Wordpress: Show related posts by tag. The tag the snippet is looking for needs to be setup in the WP admin interface using the custom value keyword = your_tag Output is as unordered list with links. Snippet is fully i8n compatible You can use this in any Wordpress Template, not just single.php

single.php

<?php
        /** SHOW RELATED POSTS BY TAG, TAG IS INDICATED BY CUSTOM PROPERTY keyword => tag **/
            
            /** check for custom property **/
            $key = 'keyword'; 
            $keyword = get_post_meta($post->ID, $key, true);
                if ($keyword != '') {
                    /** set max number of posts **/
                    $num_posts = '4';
                    /** setup the query array **/
                    $args=array(
                    /** wordpress stores spaces in custom values differently than tags, so replace them with dashes  **/        
                    'tag' => str_replace(' ', '-', $keyword),
                    'post__not_in' => array($post->ID),
                    'showposts'=>$num_posts,
                    'ignore_sticky_posts'=>1
                    );

                $original_post = $post;
                /** get tags from current post.. **/
                $tags = wp_get_post_tags($post->ID);
                /** ..and only show it if there are any ; remove the if statement if this should not get checked **/
                if ($tags) {
                /** run the query **/
                $my_query = new WP_Query($args);
                if( $my_query->have_posts() ) { 
                /** change the kubrick to textdomain of your theme **/
                /** capitilize all first letters of the tags that we're showing, remove the ucwords if you don't want that... **/
                echo '<h4 class="PostRelatedPostsHeader">', _e('Related Posts for Topic ', 'kubrick'), ucwords($keyword) . ' </h4>';?>
                <div class="PostRelatedPosts"> <ul class="related_posts">
                <?php while ($my_query->have_posts()) : $my_query->the_post();?>
            <li><a href="<?php the_permalink() ?>" rel="bookmark" title="<?php _e('Permanent Link to ', 'kubrick'); the_title_attribute(); ?>"><?php the_title();?></a>
            </li>
            <?php endwhile;?> </ul></div> <?php } } 
            /** reset the query **/
            $post = $original_post; wp_reset_query();
        }?>