The Basilisk speaks in Parseltongue that Harry can hear, saying things like "Let me rip you" "let me tear you," " I smell blood," etc. It speaks in full sentences at times.
It isn't just saying "I'm hungry", it's using threats and some creativity, using multiple synonyms (rip, tear, etc.)
There's no way that can be just a rough translation. It seems sophisticated. And yet it is controlled by the Heir? Just how intelligent is it?