The loading animation can be controlled using the 'loading' option. It defines a CSS object that you can theme. You can animated the loading display by using an animated image as the background. http://highcharts.com/ref/#loading

To change the text that it displays via the lang property of options. See http://highcharts.com/ref/#lang for more. I usually just set it to blank.

var options = {

  style: { background: 'url(/images/3044/chart_curve.png) no-repeat center' }, 

  lang: { loading: '' } 

};

var chart = new Highcharts.Chart(options);

Plus to display the CSS object, you need to call chart.showLoading();