Double issue on internationalization :

prefered title is not internationalized :

block_rss_client.php §38 is :

            $this->title = $this->config->title;

Should be :

            $this->title = format_string($this->config->title);

As a direct consequence, config_instance.html widget for preferred title is not quote protected at §123 and shows :

            $this->title = $this->config->title;

Should be :

            $this->title = htmlspecialchars($this->config->title, ENT_QUOTES, 'UTF-8');

Cheers.