RankMath SEO - Incorrect Homepage hreflang URLs in Sitemaps' Source Code

Overview of the issue

When using RankMath SEO with WPML, you might experience an issue where the homepage URLs in the sitemaps‘ source code <xhtml:link rel="alternate" hreflang="..."> are incorrect for secondary languages. Instead of showing the language-specific homepage (e.g., domain.com/?lang=es), the sitemap outputs a full page URL (e.g., domain.com/page-slug/?lang=es).

Workaround

Please, make sure of having a full site backup of your site before proceeding.

• Open the …/wp-content/plugins/wp-seo-multilingual/classes/Shared/Sitemap/BaseAlternateLangHooks.php file.
• Look for line 88.
• Replace:

  			$mapPermalink = function ( $id, $language ) use ( $getPermalink ) {
  				return apply_filters( 'wpml_permalink', $getPermalink( $id ), $language );
  			};
          

• With:

  			$mapPermalink = function ( $id, $language ) use ( $getPermalink ) {
  
  				// WPML Workaround for wpmlsupp-13368 
  				$front_id = (int) get_option( 'page_on_front' );
  				if ( $front_id ) {
  					$default_lang = apply_filters( 'wpml_default_language', null );
  					$id_in_default = (int) apply_filters( 'wpml_object_id', (int) $id, 'page', false, $default_lang );
  					if ( $id_in_default && $id_in_default === $front_id ) {
  						return apply_filters( 'wpml_permalink', trailingslashit( home_url() ), $language );
  					}
  				}
  
  				return apply_filters( 'wpml_permalink', $getPermalink( $id ), $language );
  			};
          

• Rebuild the sitemaps: Go to „Rank Math > Sitemap Settings“, change the „Links per sitemap“ value, and save.