The table sorting icons ('t/sort_asc' and 't/sort_desc') have been improved in MDL-82497, as shown below:

The report builder editor Sorting section is using a different icon - which is now exacerbated since the above change:

We should make them consistent, so that the editor uses the same icons as those use by report tables. Also note the language string is confusing because it's attempting to indicate the state of the sorting after clicking the button, whereas it looks like it's indicating the current state of the sorting

We should use language similar to this to make it clearer as to the sorting current state and the behaviour of the button:

+$string['columnsortdirectionasc'] = 'Change initial sorting for column \'{$a}\' to ascending';

+$string['columnsortdirectiondesc'] = 'Change initial sorting for column \'{$a}\' to descending';