Change label of currentRefinements item

I’m using a toggleRefinement widget to check if an item is on sale.
There is an extra attribute in my index called on_sale. It outputs true or false.

As a result my currentRefinements widget shows true or false instead of a better text like “Only on sale”.

Is there a way to change the output?

This is my current code:

  container: '#onsale',
  attribute: 'on_sale',
  templates: {
	labelText: 'Only on sale',