Index: src/wp-includes/class-wp-customize-nav-menus.php
===================================================================
--- src/wp-includes/class-wp-customize-nav-menus.php	(revision 33663)
+++ src/wp-includes/class-wp-customize-nav-menus.php	(working copy)
@@ -467,7 +467,11 @@
 		// Menu loactions.
 		$locations     = get_registered_nav_menus();
 		$num_locations = count( array_keys( $locations ) );
-		$description   = '<p>' . sprintf( _n( 'Your theme contains %s menu location. Select which menu you would like to use.', 'Your theme contains %s menu locations. Select which menu appears in each location.', $num_locations ), number_format_i18n( $num_locations ) );
+		if ( 1 == $num_locations ) {
+			$description = '<p>' . __( 'Your theme supports one menu location. Select which menu you would like to use.' );
+		} else {
+			$description = '<p>' . sprintf( _n( 'Your theme contains %s menu location. Select which menu you would like to use.', 'Your theme contains %s menu locations. Select which menu appears in each location.', $num_locations ), number_format_i18n( $num_locations ) );
+		}
 		$description  .= '</p><p>' . __( 'You can also place menus in widget areas with the Custom Menu widget.' ) . '</p>';
 
 		$this->manager->add_section( 'menu_locations', array(