Setup.
From zero to per-player translation in about four minutes.
Install Babel
Drop Babel.jar into your server's /plugins folder alongside ProtocolLib. Restart the server. Paper 1.20.4 – 1.21.x.
Create your account
Sign up at babelmc.com. No credit card, no questions.
Generate a server key
From your dashboard, create a key, give it a nickname, and copy it. The key will bind to the first server that uses it.
Paste into config.yml
Edit plugins/Babel/config.yml:
key: "bblmc_live_xxxxxxxxxxxxxxxx"
Reload and test
In-game as an op, run /babel reload then /babel lang. Pick a flag — every message the server sends you now renders in your chosen language.