diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-admin/includes/class-theme-upgrader-skin.php
--- a/wp/wp-admin/includes/class-theme-upgrader-skin.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-admin/includes/class-theme-upgrader-skin.php	Tue Dec 15 13:49:49 2020 +0100
@@ -16,10 +16,25 @@
  * @see WP_Upgrader_Skin
  */
 class Theme_Upgrader_Skin extends WP_Upgrader_Skin {
+
+	/**
+	 * Holds the theme slug in the Theme Directory.
+	 *
+	 * @since 2.8.0
+	 *
+	 * @var object
+	 */
 	public $theme = '';
 
 	/**
-	 * @param array $args
+	 * Constructor.
+	 *
+	 * Sets up the theme upgrader skin.
+	 *
+	 * @since 2.8.0
+	 *
+	 * @param array $args Optional. The theme upgrader skin arguments to
+	 *                    override default options. Default empty array.
 	 */
 	public function __construct( $args = array() ) {
 		$defaults = array(
@@ -36,12 +51,16 @@
 	}
 
 	/**
+	 * Action to perform following a single theme update.
+	 *
+	 * @since 2.8.0
 	 */
 	public function after() {
 		$this->decrement_update_count( 'theme' );
 
 		$update_actions = array();
-		if ( ! empty( $this->upgrader->result['destination_name'] ) && $theme_info = $this->upgrader->theme_info() ) {
+		$theme_info     = $this->upgrader->theme_info();
+		if ( $theme_info ) {
 			$name       = $theme_info->display( 'Name' );
 			$stylesheet = $this->upgrader->result['destination_name'];
 			$template   = $theme_info->get_template();
@@ -63,24 +82,38 @@
 				),
 				admin_url( 'customize.php' )
 			);
-			if ( get_stylesheet() == $stylesheet ) {
+
+			if ( get_stylesheet() === $stylesheet ) {
 				if ( current_user_can( 'edit_theme_options' ) && current_user_can( 'customize' ) ) {
-					$update_actions['preview']  = '<a href="' . esc_url( $customize_url ) . '" class="hide-if-no-customize load-customize">';
-					$update_actions['preview'] .= '<span aria-hidden="true">' . __( 'Customize' ) . '</span>';
-					/* translators: %s: theme name */
-					$update_actions['preview'] .= '<span class="screen-reader-text">' . sprintf( __( 'Customize &#8220;%s&#8221;' ), $name ) . '</span></a>';
+					$update_actions['preview'] = sprintf(
+						'<a href="%s" class="hide-if-no-customize load-customize">' .
+						'<span aria-hidden="true">%s</span><span class="screen-reader-text">%s</span></a>',
+						esc_url( $customize_url ),
+						__( 'Customize' ),
+						/* translators: %s: Theme name. */
+						sprintf( __( 'Customize &#8220;%s&#8221;' ), $name )
+					);
 				}
 			} elseif ( current_user_can( 'switch_themes' ) ) {
 				if ( current_user_can( 'edit_theme_options' ) && current_user_can( 'customize' ) ) {
-					$update_actions['preview']  = '<a href="' . esc_url( $customize_url ) . '" class="hide-if-no-customize load-customize">';
-					$update_actions['preview'] .= '<span aria-hidden="true">' . __( 'Live Preview' ) . '</span>';
-					/* translators: %s: theme name */
-					$update_actions['preview'] .= '<span class="screen-reader-text">' . sprintf( __( 'Live Preview &#8220;%s&#8221;' ), $name ) . '</span></a>';
+					$update_actions['preview'] = sprintf(
+						'<a href="%s" class="hide-if-no-customize load-customize">' .
+						'<span aria-hidden="true">%s</span><span class="screen-reader-text">%s</span></a>',
+						esc_url( $customize_url ),
+						__( 'Live Preview' ),
+						/* translators: %s: Theme name. */
+						sprintf( __( 'Live Preview &#8220;%s&#8221;' ), $name )
+					);
 				}
-				$update_actions['activate']  = '<a href="' . esc_url( $activate_link ) . '" class="activatelink">';
-				$update_actions['activate'] .= '<span aria-hidden="true">' . __( 'Activate' ) . '</span>';
-				/* translators: %s: theme name */
-				$update_actions['activate'] .= '<span class="screen-reader-text">' . sprintf( __( 'Activate &#8220;%s&#8221;' ), $name ) . '</span></a>';
+
+				$update_actions['activate'] = sprintf(
+					'<a href="%s" class="activatelink">' .
+					'<span aria-hidden="true">%s</span><span class="screen-reader-text">%s</span></a>',
+					esc_url( $activate_link ),
+					__( 'Activate' ),
+					/* translators: %s: Theme name. */
+					sprintf( _x( 'Activate &#8220;%s&#8221;', 'theme' ), $name )
+				);
 			}
 
 			if ( ! $this->result || is_wp_error( $this->result ) || is_network_admin() ) {
@@ -88,7 +121,11 @@
 			}
 		}
 
-		$update_actions['themes_page'] = '<a href="' . self_admin_url( 'themes.php' ) . '" target="_parent">' . __( 'Return to Themes page' ) . '</a>';
+		$update_actions['themes_page'] = sprintf(
+			'<a href="%s" target="_parent">%s</a>',
+			self_admin_url( 'themes.php' ),
+			__( 'Return to Themes page' )
+		);
 
 		/**
 		 * Filters the list of action links available following a single theme update.