Index: src/wp-admin/setup-config.php
===================================================================
--- src/wp-admin/setup-config.php	(revision 29654)
+++ src/wp-admin/setup-config.php	(working copy)
@@ -65,7 +65,7 @@
  * @since 2.3.0
  */
 function setup_config_display_header( $body_classes = array() ) {
-	global $wp_version;
+	global $wp_version, $wp_locale;
 	$body_classes = (array) $body_classes;
 	$body_classes[] = 'wp-core-ui';
 	if ( is_rtl() ) {
@@ -87,6 +87,9 @@
 <body class="<?php echo implode( ' ', $body_classes ); ?>">
 <h1 id="logo"><a href="<?php esc_attr_e( 'https://wordpress.org/' ); ?>" tabindex="-1"><?php _e( 'WordPress' ); ?></a></h1>
 <?php
+	if ( strpos( $GLOBALS['wp_version'], '-src' ) and ( 'rtl' == _x( 'ltr', 'text direction' ) ) ) {
+		$wp_locale->rtl_src_admin_notice();
+	}
 } // end function setup_config_display_header();
 
 $language = '';
@@ -110,10 +113,12 @@
 			$loaded_language = wp_download_language_pack( $language );
 			if ( $loaded_language ) {
 				load_default_textdomain( $loaded_language );
+				$GLOBALS['wp_locale'] = new WP_Locale();
 			}
 		}
 
 		setup_config_display_header();
+
 		$step_1 = 'setup-config.php?step=1';
 		if ( isset( $_REQUEST['noapi'] ) ) {
 			$step_1 .= '&amp;noapi';
@@ -144,6 +149,8 @@
 
 	case 1:
 		load_default_textdomain( $language );
+		$GLOBALS['wp_locale'] = new WP_Locale();
+
 		setup_config_display_header();
 	?>
 <form method="post" action="setup-config.php?step=2">
@@ -184,6 +191,8 @@
 
 	case 2:
 	load_default_textdomain( $language );
+	$GLOBALS['wp_locale'] = new WP_Locale();
+
 	$dbname = trim( wp_unslash( $_POST[ 'dbname' ] ) );
 	$uname = trim( wp_unslash( $_POST[ 'uname' ] ) );
 	$pwd = trim( wp_unslash( $_POST[ 'pwd' ] ) );
Index: src/wp-admin/install.php
===================================================================
--- src/wp-admin/install.php	(revision 29654)
+++ src/wp-admin/install.php	(working copy)
@@ -54,6 +54,7 @@
  * @since 2.5.0
  */
 function display_header( $body_classes = '' ) {
+	global $wp_locale;
 	header( 'Content-Type: text/html; charset=utf-8' );
 	if ( is_rtl() ) {
 		$body_classes .= 'rtl';
@@ -76,6 +77,10 @@
 <h1 id="logo"><a href="<?php echo esc_url( __( 'https://wordpress.org/' ) ); ?>" tabindex="-1"><?php _e( 'WordPress' ); ?></a></h1>
 
 <?php
+	if ( strpos( $GLOBALS['wp_version'], '-src' ) and ( 'rtl' == _x( 'ltr', 'text direction' ) ) ) {
+		$wp_locale->rtl_src_admin_notice();
+	}
+
 } // end display_header()
 
 /**
@@ -204,10 +209,12 @@
 			$loaded_language = wp_download_language_pack( $langugage );
 			if ( $loaded_language ) {
 				load_default_textdomain( $loaded_language );
+				$GLOBALS['wp_locale'] = new WP_Locale();
 			}
 		}
 
 		display_header();
+
 ?>
 <h1><?php _ex( 'Welcome', 'Howdy' ); ?></h1>
 <p><?php __( 'Welcome to the famous five-minute WordPress installation process! Just fill in the information below and you&#8217;ll be on your way to using the most extendable and powerful personal publishing platform in the world.' ); ?></p>
@@ -221,6 +228,7 @@
 	case 2:
 		if ( ! empty( $langugage ) && load_default_textdomain( $langugage ) ) {
 			$loaded_language = $langugage;
+			$GLOBALS['wp_locale'] = new WP_Locale();
 		} else {
 			$loaded_language = 'en_US';
 		}
@@ -229,6 +237,7 @@
 			wp_die( $wpdb->error->get_error_message() );
 
 		display_header();
+
 		// Fill in the data we gathered
 		$weblog_title = isset( $_POST['weblog_title'] ) ? trim( wp_unslash( $_POST['weblog_title'] ) ) : '';
 		$user_name = isset($_POST['user_name']) ? trim( wp_unslash( $_POST['user_name'] ) ) : '';
Index: src/wp-admin/css/install.css
===================================================================
--- src/wp-admin/css/install.css	(revision 29654)
+++ src/wp-admin/css/install.css	(working copy)
@@ -230,6 +230,7 @@
 	border-color: #8dff1c !important;
 }
 
+.error p,
 .message {
 	border: 1px solid #c00;
 	padding: 0.5em 0.7em;
