I suggest adding a macro that gives out the command user was running to "unknown command" error.

spigot.yml already has this:
{{
outdated-client: Outdated client! Please use

{0}
outdated-server: Outdated server! I'm still on {0}

}}

Where the macro get's replaced with version number.

I suggest adding a similar functionality to "unknown command":
{{
unknown-command: Unknown command. Type "/help" for help.
}}

Would become:

{{
unknown-command: "

{0}

" is unknown command. Type "/help" for help.
}}

This would be helpful since then you could see in server logs what commands the users were trying to run.