Since for number of reasons you may not find the name Agency discount correct, the Booking Manager now gives you the possibility to change the name of this discount.
Open Preferences > Reservation settings > Invoice (1.), find the Label for "Agency discount" (2.) and write your custom name (3.) for this discount and press Apply (4.).
Once you entered the English name of the translation (which is default for the system and therefore has to be entered) you can enter the translations in the same manner as you would for the discounts or options, click on the select (1.), choose the language (2.), write the translation (3.) and press Apply (4.).