diff --git a/src/wp-admin/options-general.php b/src/wp-admin/options-general.php
index 4ad97a531b..7011885553 100644
--- a/src/wp-admin/options-general.php
+++ b/src/wp-admin/options-general.php
@@ -305,7 +305,10 @@ endfor;
 
 <?php
 $languages = get_available_languages();
-if ( ! empty( $languages ) ) {
+if ( ! is_multisite() && defined( 'WPLANG' ) && '' !== WPLANG && 'en_US' !== WPLANG && ! in_array( WPLANG, $languages ) ) {
+	$languages[] = WPLANG;
+}
+if ( $languages ) {
 	?>
 	<tr>
 		<th width="33%" scope="row"><label for="WPLANG"><?php _e( 'Site Language' ); ?></label></th>
diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index 3828c6abc2..f307a54330 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -3361,8 +3361,12 @@ function sanitize_option($option, $value) {
 
 		case 'WPLANG':
 			$allowed = get_available_languages();
-			if ( ! in_array( $value, $allowed ) && ! empty( $value ) )
+			if ( ! is_multisite() && defined( 'WPLANG' ) && '' !== WPLANG && 'en_US' !== WPLANG ) {
+				$allowed[] = WPLANG;
+			}
+			if ( ! in_array( $value, $allowed ) && ! empty( $value ) ) {
 				$value = get_option( $option );
+			}
 			break;
 
 		case 'illegal_names':