I would say there's a difference between abstract and complex. A complex topic would take a lot of time to communicate mainly because you have to go through all the prerequisites. By abstract I mean something like "communicate" or "loss" or "zero"! The primitives of complex thought.

And if we're saying the lion can speak human, then I think it follows that they're capable of this abstract thought, which is what I think is making the premise confusing for me. Maybe if I change my thinking and let's just say the lion is speaking... But if they're speaking a "language" that's capable of communicating concrete and abstract concepts, then that's a human-style language! And because we share many concrete concepts in our shared life experience, I think we would be able to communicate concrete concepts, and then use those as proxies to communicate abstract concepts and hence all concepts?