How to enable WFAS Formations in Warband

1- Open the chosen module folder (for instance: MountBlade Warband/Modules/Native);
2- Open your module.ini;
3- Scroll to bottom or search for the string "use_advanced_formation", set it to 1;
4- If there is no "use_advanced_formation" at the bottom, add a line at the bottom of the module.ini and put "use_advanced_formation = 1"

That alone will enable the formations but the UI may not display properly, at which case you should do the following steps:

1- Still in your module folder, open Languagues/en;
2- Open the ui.csv with a notepad program;
3- Copy and paste this at the bottom of the file:

ui_cut|Cutting
ui_pierce|Piercing
ui_blunt|Blunt
ui_use_melee_weapons_e_|Use melee weapons!
ui_use_ranged_weapons_e_|Use ranged weapons!
ui_order_button_use_melee_weapons|Use melee weapons
ui_order_button_use_ranged_weapons|Use ranged weapons
ui_order_button_weapon_usage_orders|Weapon usage orders
ui_fire_at_my_command_e_|Fire at my command!
ui_fire_now_e_|Fire now!
ui_order_button_fire_at_my_command|Fire at my command
ui_order_button_fire_now|Fire now
ui_order_form_1_row|Form 1 row
ui_order_form_2_row|Form 2 rows
ui_order_form_3_row|Form 3 rows
ui_order_form_4_row|Form 4 rows
ui_order_form_5_row|Form 5 rows
ui_form_1_row_e_|Form 1 row!
ui_form_2_row_e_|Form 2 rows!
ui_form_3_row_e_|Form 3 rows!
ui_form_4_row_e_|Form 4 rows!
ui_form_5_row_e_|Form 5 rows!
ui_order_7|Select Order 7
ui_order_8|Select Order 8
ui_all_fire_now_e_|All fire now!
ui_left_fire_now_e_|Left flank fire now!
ui_middle_fire_now_e_|Middle group fire now!
ui_right_fire_now_e_|Right flank fire now!
ui_order_button_all_fire_now|All fire now
ui_order_button_left_fire_now|Left flank fire now
ui_order_button_middle_fire_now|Middle group fire now
ui_order_button_right_fire_now|Right flank fire now
ui_crouch|Crouch

Press one Enter below Crouch so as to give it an empty line below it, otherwise the last letter of Crouch gets eaten for some reason