I suggest that you put these two lines of code (included in wp-seo.php) in a function called by the init action to improve compatibility with other plugins:
load_plugin_textdomain( 'wordpress-seo', false, dirname( plugin_basename( __FILE__ ) ) . '/languages' );
As it is, load_plugin_textdomain is executed too soon and prevents multilingual plugins (I tested with WP Native Dashboard, qtranslate & Polylang) to translate your admin interface when the user switches the admin language to the non default WordPress language.
$options = get_wpseo_options();
See reasons here.