Uncaught Error: Call to undefined function WPMLBlockEditor::wp_enqueue_block_style()

Overview of the issue

Using version of WordPress lower than 5.9.0 with WPML 4.6.9 can result in a fatal error:

Uncaught Error: Call to undefined function WPMLBlockEditor::wp_enqueue_block_style() in /wp-content/plugins/sitepress-multilingual-cms/classes/block-editor/Loader.php:97

Workaround

You can downgrade to WPML 4.6.8, try the beta version of WPML V4.6.10, or use the directions below to patch the code until a permanent fix is issued. Please make sure you have a full backup of your site before you modify any code.

Go to: wp-content/plugins/sitepress-multilingual-cms/classes/block-editor/Loader.php and look for the method WPMLBlockEditorLoader::maybeEnqueueNavigationBlockStyles replace it with:

	public function maybeEnqueueNavigationBlockStyles() {
		global $wp_version;
		if ( version_compare($wp_version, '5.9.0' ) >= 0) {
			if ( ! wp_style_is( 'wp-block-navigation', 'enqueued' ) || ! wp_style_is( 'wp-block-navigation', 'queue' ) ) {
				wp_enqueue_block_style( LanguageSwitcher::BLOCK_LANGUAGE_SWITCHER, [
					'handle' => 'wp-block-navigation'
				] );
			}
		}
	}