diff --git a/wp-includes/class.wp-scripts.php b/wp-includes/class.wp-scripts.php
index e843233cbc..26fbd6da9b 100644
--- a/wp-includes/class.wp-scripts.php
+++ b/wp-includes/class.wp-scripts.php
@@ -499,14 +499,14 @@ class WP_Scripts extends WP_Dependencies {
 	 * Sets a translation textdomain.
 	 *
 	 * @since 5.0.0
+	 * @since 5.1.0 The `$domain` parameter was made optional.
 	 *
 	 * @param string $handle Name of the script to register a translation domain to.
-	 * @param string $domain The textdomain.
+	 * @param string $domain Optional. Text domain. Default 'default'.
 	 * @param string $path   Optional. The full file path to the directory containing translation files.
-	 *
-	 * @return bool True if the textdomain was registered, false if not.
+	 * @return bool True if the text domain was registered, false if not.
 	 */
-	public function set_translations( $handle, $domain, $path = null ) {
+	public function set_translations( $handle, $domain = 'default', $path = null ) {
 		if ( ! isset( $this->registered[ $handle ] ) ) {
 			return false;
 		}
@@ -517,6 +517,7 @@ class WP_Scripts extends WP_Dependencies {
 		if ( ! in_array( 'wp-i18n', $obj->deps, true ) ) {
 			$obj->deps[] = 'wp-i18n';
 		}
+
 		return $obj->set_translations( $domain, $path );
 	}
 
diff --git a/wp-includes/functions.wp-scripts.php b/wp-includes/functions.wp-scripts.php
index 5aa26cca5e..2e99067f90 100644
--- a/wp-includes/functions.wp-scripts.php
+++ b/wp-includes/functions.wp-scripts.php
@@ -209,14 +209,14 @@ function wp_localize_script( $handle, $object_name, $l10n ) {
  * @global WP_Scripts $wp_scripts The WP_Scripts object for printing scripts.
  *
  * @since 5.0.0
+ * @since 5.1.0 The `$domain` parameter was made optional.
  *
  * @param string $handle Script handle the textdomain will be attached to.
- * @param string $domain The textdomain.
+ * @param string $domain Optional. Text domain. Default 'default'.
  * @param string $path   Optional. The full file path to the directory containing translation files.
- *
- * @return bool True if the textdomain was successfully localized, false otherwise.
+ * @return bool True if the text domain was successfully localized, false otherwise.
  */
-function wp_set_script_translations( $handle, $domain, $path = null ) {
+function wp_set_script_translations( $handle, $domain = 'default', $path = null ) {
 	global $wp_scripts;
 	if ( ! ( $wp_scripts instanceof WP_Scripts ) ) {
 		_wp_scripts_maybe_doing_it_wrong( __FUNCTION__ );
diff --git a/wp-includes/l10n.php b/wp-includes/l10n.php
index 7dd86607ec..fb88ba5e07 100644
--- a/wp-includes/l10n.php
+++ b/wp-includes/l10n.php
@@ -898,17 +898,18 @@ function load_child_theme_textdomain( $domain, $path = false ) {
  *
  * @since 5.0.0
  * @since 5.0.2 Uses load_script_translations() to load translation data.
+ * @since 5.1.0 The `$domain` parameter was made optional.
  *
  * @see WP_Scripts::set_translations()
  *
  * @param string $handle Name of the script to register a translation domain to.
- * @param string $domain The text domain.
+ * @param string $domain Optional. Text domain. Default 'default'.
  * @param string $path   Optional. The full file path to the directory containing translation files.
  *
  * @return false|string False if the script textdomain could not be loaded, the translated strings
  *                      in JSON encoding otherwise.
  */
-function load_script_textdomain( $handle, $domain, $path = null ) {
+function load_script_textdomain( $handle, $domain = 'default', $path = null ) {
 	$wp_scripts = wp_scripts();
 
 	if ( ! isset( $wp_scripts->registered[ $handle ] ) ) {
diff --git a/wp-includes/script-loader.php b/wp-includes/script-loader.php
index 7f745acffd..bc21f9cbac 100644
--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -466,16 +466,16 @@ function wp_default_packages_scripts( &$scripts ) {
 	);
 
 	$package_translations = array(
-		'api-fetch'            => 'default',
-		'blocks'               => 'default',
-		'block-library'        => 'default',
-		'components'           => 'default',
-		'edit-post'            => 'default',
-		'editor'               => 'default',
-		'format-library'       => 'default',
-		'keycodes'             => 'default',
-		'list-reusable-blocks' => 'default',
-		'nux'                  => 'default',
+		'api-fetch',
+		'blocks',
+		'block-library',
+		'components',
+		'edit-post',
+		'editor',
+		'format-library',
+		'keycodes',
+		'list-reusable-blocks',
+		'nux',
 	);
 
 	foreach ( $packages_dependencies as $package => $dependencies ) {
@@ -485,8 +485,8 @@ function wp_default_packages_scripts( &$scripts ) {
 
 		$scripts->add( $handle, $path, $dependencies, $version, 1 );
 
-		if ( isset( $package_translations[ $package ] ) ) {
-			$scripts->set_translations( $handle, $package_translations[ $package ] );
+		if ( in_array( $package, $package_translations, true ) ) {
+			$scripts->set_translations( $handle );
 		}
 	}
 }
diff --git a/wp-includes/version.php b/wp-includes/version.php
index df9cff38fb..f0fd2bed0a 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44394';
+$wp_version = '5.1-alpha-44395';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.