How to prevent behavior-attached functions from being attached twice?
The once() function will help with that,e.g.

(function($) { 
   Drupal.behaviors.mymodule = {
    attach: function (context, settings) {

      $('.skip-line', context).once('mymodule').on('change', function(){
        // some code
        if ( confirm(Drupal.t('Apply to all languages?')) ) {
          // applying...
        }
      });
    }
  };
})(jQuery);


One of the many references