diff --git a/wp-includes/l10n.php b/wp-includes/l10n.php
index b4f1701fe7..3b99ff848b 100644
--- a/wp-includes/l10n.php
+++ b/wp-includes/l10n.php
@@ -728,6 +728,10 @@ function load_textdomain( $domain, $mofile, $locale = null ) {
 
 	$l10n_unloaded = (array) $l10n_unloaded;
 
+	if ( ! is_string( $domain ) ) {
+		return false;
+	}
+
 	/**
 	 * Filters whether to short-circuit loading .mo file.
 	 *
@@ -989,6 +993,10 @@ function load_plugin_textdomain( $domain, $deprecated = false, $plugin_rel_path
 	/** @var WP_Textdomain_Registry $wp_textdomain_registry */
 	global $wp_textdomain_registry;
 
+	if ( ! is_string( $domain ) ) {
+		return false;
+	}
+
 	/**
 	 * Filters a plugin's locale.
 	 *
@@ -1037,6 +1045,10 @@ function load_muplugin_textdomain( $domain, $mu_plugin_rel_path = '' ) {
 	/** @var WP_Textdomain_Registry $wp_textdomain_registry */
 	global $wp_textdomain_registry;
 
+	if ( ! is_string( $domain ) ) {
+		return false;
+	}
+
 	/** This filter is documented in wp-includes/l10n.php */
 	$locale = apply_filters( 'plugin_locale', determine_locale(), $domain );
 
@@ -1076,6 +1088,10 @@ function load_theme_textdomain( $domain, $path = false ) {
 	/** @var WP_Textdomain_Registry $wp_textdomain_registry */
 	global $wp_textdomain_registry;
 
+	if ( ! is_string( $domain ) ) {
+		return false;
+	}
+
 	/**
 	 * Filters a theme's locale.
 	 *
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 1b68a025e6..701e4cc208 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-alpha-57924';
+$wp_version = '6.6-alpha-57925';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.