diff --git a/src/wp-admin/install.php b/src/wp-admin/install.php
index a24baff3b6..0021421007 100644
--- a/src/wp-admin/install.php
+++ b/src/wp-admin/install.php
@@ -281,7 +281,7 @@ if ( defined( 'DO_NOT_UPGRADE_GLOBAL_TABLES' ) ) {
  */
 $language = '';
 if ( ! empty( $_REQUEST['language'] ) ) {
-	$language = preg_replace( '/[^a-zA-Z_]/', '', $_REQUEST['language'] );
+	$language = preg_replace( '/[^a-zA-Z0-9_]/', '', $_REQUEST['language'] );
 } elseif ( isset( $GLOBALS['wp_local_package'] ) ) {
 	$language = $GLOBALS['wp_local_package'];
 }
diff --git a/src/wp-admin/setup-config.php b/src/wp-admin/setup-config.php
index db10e25be2..c1fe1eb808 100644
--- a/src/wp-admin/setup-config.php
+++ b/src/wp-admin/setup-config.php
@@ -105,7 +105,7 @@ function setup_config_display_header( $body_classes = array() ) {
 
 $language = '';
 if ( ! empty( $_REQUEST['language'] ) ) {
-	$language = preg_replace( '/[^a-zA-Z_]/', '', $_REQUEST['language'] );
+	$language = preg_replace( '/[^a-zA-Z0-9_]/', '', $_REQUEST['language'] );
 } elseif ( isset( $GLOBALS['wp_local_package'] ) ) {
 	$language = $GLOBALS['wp_local_package'];
 }