Not sure if this was answered but I'm doing it anyway:
Language-specific? Like Localization? Now I'm curious. Can I make a menu with 'variables' for displayed words, so something like "%main %menu" would be displayed as "'Main Menu" using a default lang file, but it would be displayed as "|\/|41|\| |\/|3Nu" using the 'l33t' lang file?
No, it means that you can have subdirectories in the menu folder and when you type "menu main" it will load the menu from pball/menus/<language>/
<language> will be replace with the value of the cl_language cvar.