Sorry I solved it!
I idiotically had made a folder for the subdirectory I wanted in a previous attempt like:
/public_html/addonsite.com/cn
don’t know why I did, read it somewhere,,
but this tripped up the request for addonsite.com/cn to just show this folder instead of wordpress’ magic. deleted the folder, and presto this finally works, awesome
sorry for false alarm, cheers!