Add support for WPML post locale

integration/class-wpml.php

@@ -0,0 +1,41 @@
+<?php
+/**
+ * WPML integration.
+ *
+ * @package Activitypub
+ */
+
+namespace Activitypub\Integration;
+
+/**
+ * Compatibility with the WPML Multilingual CMS plugin.
+ *
+ * @see https://wpml.org/
+ */
+class WPML {
+	/**
+	 * Initialize the class, registering WordPress hooks.
+	 */
+	public static function init() {
+		\add_filter( 'activitypub_post_locale', array( self::class, 'get_wpml_post_locale' ), 10, 3 );
+	}
+
+	/**
+	 * Fetch the post locale from the WPML post data.
+	 *
+	 * @param string          $lang    The language code.
+	 * @param int             $post_id The post ID.
+	 * @param WP_Post         $post    The post object
+	 *
+	 * @return string The modified language code.
+	 */
+	public static function get_wpml_post_locale( $lang, $post_id, $post ) {
+		$language_details = apply_filters( 'wpml_post_language_details', NULL, $post_id );
+
+		if ( is_array( $language_details ) && isset( $language_details['language_code'] ) ) {
+			$lang = $language_details['language_code'];
+		}
+
+		return $lang;
+	}
+}

integration/load.php

@@ -100,6 +100,17 @@ function ( $transformer, $data, $object_class ) {
 			3
 		);
 	}
+
+	/**
+	 * Adds WPML Multilingual CMS (plugin) support.
+	 *
+	 * This class handles the compatibility with the WPML plugin.
+	 *
+	 * @see https://wpml.org/
+	 */
+	if ( \defined( 'ICL_SITEPRESS_VERSION' ) ) {
+		WPML::init();
+	}
 }
 \add_action( 'plugins_loaded', __NAMESPACE__ . '\plugin_init' );