Index: src/wp-includes/customize/class-wp-customize-nav-menu-control.php
===================================================================
--- src/wp-includes/customize/class-wp-customize-nav-menu-control.php	(revision 42199)
+++ src/wp-includes/customize/class-wp-customize-nav-menu-control.php	(working copy)
@@ -35,11 +35,20 @@
 	 * @since 4.3.0
 	 */
 	public function content_template() {
+		$add_items = __( 'Add Items' );
 		?>
-		<p class="new-menu-item-invitation"><?php _e( 'Time to add some links! Click &#8220;Add menu items&#8221; to start putting pages, categories, and custom links in your menu. Add as many things as you&#8217;d like.' ); ?></p>
+		<p class="new-menu-item-invitation">
+			<?php
+			echo esc_html( sprintf(
+				/* translators: %s: "Add Items" button text */
+				__( 'Time to add some links! Click &#8220;%s&#8221; to start putting pages, categories, and custom links in your menu. Add as many things as you&#8217;d like.' ),
+				$add_items
+			) );
+			?>
+		</p>
 		<div class="customize-control-nav_menu-buttons">
 			<button type="button" class="button add-new-menu-item" aria-label="<?php esc_attr_e( 'Add or remove menu items' ); ?>" aria-expanded="false" aria-controls="available-menu-items">
-				<?php _e( 'Add Items' ); ?>
+				<?php echo esc_html( $add_items ); ?>
 			</button>
 			<button type="button" class="button-link reorder-toggle" aria-label="<?php esc_attr_e( 'Reorder menu items' ); ?>" aria-describedby="reorder-items-desc-{{ data.menu_id }}">
 				<span class="reorder"><?php _e( 'Reorder' ); ?></span>