Oh my God, that was (more or less) it.
/ping returned the “unknown command” text.
/marcar returned the “unknown command” text. This is the command they show on the help screen, and it means “to mark”.
But then, when I was double checking that I have the ping system active and such, I noticed they call the system on the options screen “Sistema de avisos” (or “Warning/call system”).
So I tried /aviso and there you go. That’s the command in spanish.
I’m kind of relieved and furious at the same time 
Thanks for the help, both of you!