Highcharts: Format all numbers with comma?

This can be set with the thousandSep (API) global option.

Highcharts.setOptions({
    lang: {
        thousandsSep: ','
    }
});

See this JSFiddle example.

This way worked with me.

I configured in yAxis option.

yAxis: {
  labels: {
    formatter: function() {
        return Highcharts.numberFormat(this.value, 2);
    }
  }
}