The latest https://github.com/fiatjaf/nak release (v0.16.2) comes with an --outbox flag to "nak req", which means you don't have to specify relays in your filter and relays from specific authors will be used (filters will be smartly split).

Which means you can, for example, get all pubkeys who have published to wss://lang.relays.land/es then go to each of their own outbox relay, fetch their new notes live and publish those to wss://lang.relays.land/es.

nak req -l 10000 lang.relays.land/es | jq --slurp 'map(.pubkey) | unique | {authors: .}' | nak req --since '1 hour ago' -k 1 --outbox -n 3 --stream | nak event lang.relays.land/es