Cómo combinar "Elegir carpeta comando" con la función "agregar elementos de la carpeta" con Applescript

Acaba de quitar el controlador y el cambio de la variable "these_items" para "this_folder", así:

set this_folder to choose folder with prompt "Select source folder:" with multiple selections allowed
set target_folder to choose folder with prompt "Select backup folder:"

tell application "Finder" to duplicate this_folder to target_folder

A continuación, ejecute la secuencia de comandos como un script normal, y se copia en la carpeta enteramente a su destino.

Si, por otro lado, usted sólo desea que los elementos a ser copiado (no la carpeta), podría utilizar esta variación:

set this_folder to choose folder with prompt "Select source folder:" with multiple selections allowed
set target_folder to choose folder with prompt "Select backup folder:"

tell application "Finder"
    set these_items to list folder of this_folder without invisibles
    repeat with i from 1 to count of these_items
        set ItemX to item i of these_items
        set ItemX to (this_folder & ItemX as string) as alias
        duplicate ItemX to target_folder
    end repeat
end tell

De cualquier manera, usted podría terminar con un duplicado de los contenidos de la carpeta.

Ahora, teniendo en cuenta sus comentarios a continuación, esta versión va a ejecutar el script como una carpeta acción, pero recuerde que su carpeta de destino cuando se declara una propiedad en el comienzo de la secuencia de comandos. Si vuelve a compilar el script, a preguntar de nuevo.

property target_folder : ""

on adding folder items to this_folder after receiving these_items
    if target_folder = "" then
        set target_folder to ¬
            choose folder with prompt "Select source folder:" with multiple selections allowed
    else
        try
            --if the script has a property that has been deleted (i.e., the destination folder), it will cause 
            --an error that resolves by asking for a new folder
            set target_folder to target_folder as alias
        on error
            set target_folder to ¬
                ¬
                    choose folder with prompt "Select source folder:" with multiple selections allowed
        end try
    end if
    tell application "Finder" to duplicate these_items to folder target_folder
end adding folder items to

Espero que esto ayude.