'columnsortenabled' is currently 'Enable sorting for column {$a}' and 'columnsortdisabled' is 'Disable sorting for column {$a}'

This suggests that that the checkbox on the column in the reportbuilder UI that uses these language strings would enable/disable the ability to sort that column completely, i.e. if it were disabled you would be unable to click on the column and sort by it in the view mode.

However this is not what the checkbox toggles, instead it enables the column for the default sorting order in the report, and regardless of the checkbox being ticked or not the ability to sort the column is always enabled.