diff --git a/wp-includes/class-wp-textdomain-registry.php b/wp-includes/class-wp-textdomain-registry.php
index b2cbd72fa5..113ef3bd65 100644
--- a/wp-includes/class-wp-textdomain-registry.php
+++ b/wp-includes/class-wp-textdomain-registry.php
@@ -314,6 +314,7 @@ class WP_Textdomain_Registry {
 
 				if ( $file_path === $mo_path || $file_path === $php_path ) {
 					$found_location = rtrim( $location, '/' ) . '/';
+					break 2;
 				}
 			}
 		}
diff --git a/wp-includes/l10n.php b/wp-includes/l10n.php
index 8191b88cee..38c30b84e8 100644
--- a/wp-includes/l10n.php
+++ b/wp-includes/l10n.php
@@ -1435,19 +1435,20 @@ function translate_user_role( $name, $domain = 'default' ) {
 }
 
 /**
- * Gets all available languages based on the presence of *.mo files in a given directory.
+ * Gets all available languages based on the presence of *.mo and *.l10n.php files in a given directory.
  *
  * The default directory is WP_LANG_DIR.
  *
  * @since 3.0.0
  * @since 4.7.0 The results are now filterable with the {@see 'get_available_languages'} filter.
+ * @since 6.5.0 The initial file list is now cached and also takes into account *.l10n.php files.
  *
  * @global WP_Textdomain_Registry $wp_textdomain_registry WordPress Textdomain Registry.
  *
  * @param string $dir A directory to search for language files.
  *                    Default WP_LANG_DIR.
  * @return string[] An array of language codes or an empty array if no languages are present.
- *                  Language codes are formed by stripping the .mo extension from the language file names.
+ *                  Language codes are formed by stripping the file extension from the language file names.
  */
 function get_available_languages( $dir = null ) {
 	global $wp_textdomain_registry;
@@ -1460,6 +1461,8 @@ function get_available_languages( $dir = null ) {
 	if ( $lang_files ) {
 		foreach ( $lang_files as $lang_file ) {
 			$lang_file = basename( $lang_file, '.mo' );
+			$lang_file = basename( $lang_file, '.l10n.php' );
+
 			if ( ! str_starts_with( $lang_file, 'continents-cities' ) && ! str_starts_with( $lang_file, 'ms-' ) &&
 				! str_starts_with( $lang_file, 'admin-' ) ) {
 				$languages[] = $lang_file;
@@ -1475,7 +1478,7 @@ function get_available_languages( $dir = null ) {
 	 * @param string[] $languages An array of available language codes.
 	 * @param string   $dir       The directory where the language files were found.
 	 */
-	return apply_filters( 'get_available_languages', $languages, $dir );
+	return apply_filters( 'get_available_languages', array_unique( $languages ), $dir );
 }
 
 /**
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 18981e3495..3ee45a5b55 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.5-beta1-57638';
+$wp_version = '6.5-beta1-57639';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.