This question already has an answer here:
The Enterprise-D's computer shows us on multiple occasions that it can deal with natural language input. One notable example of extended conversation is in TNG '11001010':
PICARD: Computer, explain Red Alert.
COMPUTER: Initiated as a programmed response. The magnetic field containing the antimatter had weakened. There was no fail-safe available.
PICARD: Why wasn't I notified?
PICARD: Present condition?
COMPUTER: The magnetic field is now restored. Containment is restored. Propulsion is at maximum efficiency.
This continues for a while, so I shan't bore you with the details.
The Computer can even deal with Lwaxana Troi's talking to it as if it were a person:
LWAXANA: Hello, computer? Is Commander Riker still on the Bridge?
COMPUTER: Negative. Riker is currently in holodeck three.
LWAXANA: Holodeck? Where is that?
COMPUTER: Follow the comm. panel lights. They will lead you there.
So, if the computer can deal with natural language requests, why does Picard order 'Tea. Earl Grey. Hot.' rather than something more like 'Replicate a cup of hot Earl Grey tea?'