Step-by-Step Solution

To solve this type of code-word puzzle, we first need to determine the answer in plain English and then find the corresponding code word for that answer from the given list.

1. Find the Real-World Answer

The question asks, "Then where does aeroplane fly?". In the real world, aeroplanes fly in the sky.

2. Find the Code for the Answer

Now, we look at the provided code list to see what "sky" is called in this specific language.

The last part of the code states: "...'sky' is called 'sea'."

Conclusion

Therefore, in this coded language, aeroplanes fly in the sea.