how to translate the search filter default options text

we’ll make this an option in coming releases via the settings page, otherwise you need something like this to add to your theme functions.php file:

function em_wpfullcalendar_category_label($taxonomy_args,$taxonomy){
 if ( $taxonomy->name == 'event-categories'){
  $taxonomy_args['show_option_all'] = 'All Cats';
 }
 return $taxonomy_args;
}
add_filter('wpmfc_calendar_taxonomy_args','em_wpfullcalendar_category_label',1,2);