TOPIC: WBS Dictionary

Does the code of Account Identifier have to be unique on each of the WBS Dictionary?

Absolutely Yes.
for each activity there will be unique identifier.
no two more activities have same identifier.
if we give two activities the same identifier then
it will leads us to conflicts.

Actually I wanted to ask the account identifier not activity identifier. I think that it is not easy to open account id for each of the activity. Isn't it?

Yes this should be different for all work packages as this can help the company accounting system to make sure the payment is made