diff --git a/wp-includes/l10n/class-wp-translation-file.php b/wp-includes/l10n/class-wp-translation-file.php
index 93842bec10..e6dbdb85be 100644
--- a/wp-includes/l10n/class-wp-translation-file.php
+++ b/wp-includes/l10n/class-wp-translation-file.php
@@ -207,7 +207,7 @@ abstract class WP_Translation_File {
 	}
 
 	/**
-	 * Returns the plural form for a count.
+	 * Returns the plural form for a given number.
 	 *
 	 * @since 6.5.0
 	 *
@@ -219,9 +219,9 @@ abstract class WP_Translation_File {
 			$this->parse_file();
 		}
 
-		// In case a plural form is specified as a header, but no function included, build one.
 		if ( null === $this->plural_forms && isset( $this->headers['plural-forms'] ) ) {
-			$this->plural_forms = $this->make_plural_form_function( $this->headers['plural-forms'] );
+			$expression         = $this->get_plural_expression_from_header( $this->headers['plural-forms'] );
+			$this->plural_forms = $this->make_plural_form_function( $expression );
 		}
 
 		if ( is_callable( $this->plural_forms ) ) {
@@ -231,6 +231,7 @@ abstract class WP_Translation_File {
 			 * @var int $result Plural form.
 			 */
 			$result = call_user_func( $this->plural_forms, $number );
+
 			return $result;
 		}
 
@@ -238,6 +239,22 @@ abstract class WP_Translation_File {
 		return ( 1 === $number ? 0 : 1 );
 	}
 
+	/**
+	 * Returns the plural forms expression as a tuple.
+	 *
+	 * @since 6.5.0
+	 *
+	 * @param string $header Plural-Forms header string.
+	 * @return string Plural forms expression.
+	 */
+	protected function get_plural_expression_from_header( $header ) {
+		if ( preg_match( '/^\s*nplurals\s*=\s*(\d+)\s*;\s+plural\s*=\s*(.+)$/', $header, $matches ) ) {
+			return trim( $matches[2] );
+		}
+
+		return 'n != 1';
+	}
+
 	/**
 	 * Makes a function, which will return the right translation index, according to the
 	 * plural forms header.
@@ -247,7 +264,7 @@ abstract class WP_Translation_File {
 	 * @param string $expression Plural form expression.
 	 * @return callable(int $num): int Plural forms function.
 	 */
-	public function make_plural_form_function( string $expression ): callable {
+	protected function make_plural_form_function( string $expression ): callable {
 		try {
 			$handler = new Plural_Forms( rtrim( $expression, ';' ) );
 			return array( $handler, 'get' );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b3a409ecf6..e78f96755c 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.5-alpha-57517';
+$wp_version = '6.5-alpha-57518';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.