Alright luffy unlocked this ability as a
child.
If you remember when he started sensing for natural energy.
This ability only allowed him to speak to plants.But now that he obsorbed so much natural energy.
He has become intuned with nature through his near death experience caused by obsorbing.
Too much natural energy at once and because he did it twice in such a short time frame.
It changed his body permanently.
This allowed him to hear the thoughts of the shark.Through his connection with nature.
It's almost like the voice of all things but stronger as luffy can communicate with nature itself.
He could probably communicate.With fruits vegetables and even possibly the sea itself.
That's it for now I will be giving an updated version of luffy's.And the other straw hats power levels very soon.