diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 01d8a88bb4..c00e34da9d 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -5342,8 +5342,12 @@ function wp_auth_check_html() {
 	<?php
 
 	if ( $same_domain ) {
+		$login_src = add_query_arg( array(
+			'interim-login' => '1',
+			'wp_lang'       => get_user_locale(),
+		), $login_url );
 		?>
-		<div id="wp-auth-check-form" class="loading" data-src="<?php echo esc_url( add_query_arg( array( 'interim-login' => 1 ), $login_url ) ); ?>"></div>
+		<div id="wp-auth-check-form" class="loading" data-src="<?php echo esc_url( $login_src ); ?>"></div>
 		<?php
 	}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3ddb235e2c..9e10fc8fc8 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-41691';
+$wp_version = '4.9-alpha-41692';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-login.php b/wp-login.php
index 869502414b..4ae5f161a6 100644
--- a/wp-login.php
+++ b/wp-login.php
@@ -425,12 +425,16 @@ setcookie( TEST_COOKIE, 'WP Cookie check', 0, COOKIEPATH, COOKIE_DOMAIN, $secure
 if ( SITECOOKIEPATH != COOKIEPATH )
 	setcookie( TEST_COOKIE, 'WP Cookie check', 0, SITECOOKIEPATH, COOKIE_DOMAIN, $secure );
 
+$lang            = ! empty( $_GET['wp_lang'] ) ? sanitize_text_field( $_GET['wp_lang'] ) : '';
+$switched_locale = switch_to_locale( $lang );
+
 /**
  * Fires when the login form is initialized.
  *
  * @since 3.2.0
  */
 do_action( 'login_init' );
+
 /**
  * Fires before a specified login form action.
  *
@@ -484,6 +488,10 @@ case 'postpass' :
 	}
 	setcookie( 'wp-postpass_' . COOKIEHASH, $hasher->HashPassword( wp_unslash( $_POST['post_password'] ) ), $expire, COOKIEPATH, COOKIE_DOMAIN, $secure );
 
+	if ( $switched_locale ) {
+	    restore_previous_locale();
+	}
+
 	wp_safe_redirect( wp_get_referer() );
 	exit();
 
@@ -501,6 +509,10 @@ case 'logout' :
 		$requested_redirect_to = '';
 	}
 
+	if ( $switched_locale ) {
+	    restore_previous_locale();
+	}
+
 	/**
 	 * Filters the log out redirect URL.
 	 *
@@ -589,6 +601,11 @@ endif;
 
 <?php
 login_footer('user_login');
+
+if ( $switched_locale ) {
+    restore_previous_locale();
+}
+
 break;
 
 case 'resetpass' :
@@ -713,6 +730,11 @@ endif;
 
 <?php
 login_footer('user_pass');
+
+if ( $switched_locale ) {
+    restore_previous_locale();
+}
+
 break;
 
 case 'register' :
@@ -788,6 +810,11 @@ case 'register' :
 
 <?php
 login_footer('user_login');
+
+if ( $switched_locale ) {
+    restore_previous_locale();
+}
+
 break;
 
 case 'login' :
@@ -1031,5 +1058,10 @@ try {
 
 <?php
 login_footer();
+
+if ( $switched_locale ) {
+    restore_previous_locale();
+}
+
 break;
 } // end action switch