How do I restrict languages - either allow or deny list

[loopiv]

I'm trying to restrict messages by languages using rspamd. For example, I can't seem to allow english (en) or deny certain ones such as japanese (ja) or chinese (zh). I've tried looking at https://rspamd.com/doc/lua/examples.html and postalserver/postal#1754 but can't seem to get the right sauce. Thanks in advance!