What can be used to implement a chatbot in an iOS application?

Question

iOS

It is necessary to implement a chatbot in English in an iPhone application. The topics of the dialogues are as wide as possible.

Questions from users can be of the following kind:
"What is you favorite meal?", "Who discovered America?", "How was your day?", "Tell me about this" should be answered.

The goal is to engage in dialogue and answer questions.

What would you recommend for this task.