diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-includes/feed-rss2-comments.php
--- a/wp/wp-includes/feed-rss2-comments.php	Tue Jun 09 11:14:17 2015 +0000
+++ b/wp/wp-includes/feed-rss2-comments.php	Mon Oct 14 17:39:30 2019 +0200
@@ -5,7 +5,7 @@
  * @package WordPress
  */
 
-header('Content-Type: ' . feed_content_type('rss-http') . '; charset=' . get_option('blog_charset'), true);
+header('Content-Type: ' . feed_content_type('rss2') . '; charset=' . get_option('blog_charset'), true);
 
 echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>';
 
@@ -33,17 +33,24 @@
 >
 <channel>
 	<title><?php
-		if ( is_singular() )
+		if ( is_singular() ) {
+			/* translators: Comments feed title. 1: Post title */
 			printf( ent2ncr( __( 'Comments on: %s' ) ), get_the_title_rss() );
-		elseif ( is_search() )
+		} elseif ( is_search() ) {
+			/* translators: Comments feed title. 1: Site name, 2: Search query */
 			printf( ent2ncr( __( 'Comments for %1$s searching on %2$s' ) ), get_bloginfo_rss( 'name' ), get_search_query() );
-		else
-			printf( ent2ncr( __( 'Comments for %s' ) ), get_bloginfo_rss( 'name' ) . get_wp_title_rss() );
+		} else {
+			/* translators: Comments feed title. 1: Site name */
+			printf( ent2ncr( __( 'Comments for %s' ) ), get_wp_title_rss() );
+		}
 	?></title>
 	<atom:link href="<?php self_link(); ?>" rel="self" type="application/rss+xml" />
 	<link><?php (is_single()) ? the_permalink_rss() : bloginfo_rss("url") ?></link>
 	<description><?php bloginfo_rss("description") ?></description>
-	<lastBuildDate><?php echo mysql2date('r', get_lastcommentmodified('GMT')); ?></lastBuildDate>
+	<lastBuildDate><?php
+		$date = get_lastcommentmodified( 'GMT' );
+		echo $date ? mysql2date( 'r', $date, false ) : date( 'r' );
+	?></lastBuildDate>
 	<sy:updatePeriod><?php
 		/** This filter is documented in wp-includes/feed-rss2.php */
 		echo apply_filters( 'rss_update_period', 'hourly' );
@@ -69,8 +76,10 @@
 				$title = get_the_title($comment_post->ID);
 				/** This filter is documented in wp-includes/feed.php */
 				$title = apply_filters( 'the_title_rss', $title );
+				/* translators: Individual comment title. 1: Post title, 2: Comment author name */
 				printf(ent2ncr(__('Comment on %1$s by %2$s')), $title, get_comment_author_rss());
 			} else {
+				/* translators: Comment author title. 1: Comment author name */
 				printf(ent2ncr(__('By: %s')), get_comment_author_rss());
 			}
 		?></title>