I've found two ways to integrate a Dialogflow chatbot on an Ionic app.

1. The easiest way

This way can take you maximum 3 minutes to integrate a Dialogflow chatbot, really!

Since Dialogflow exposes a web bot demo, we can simply add an iframe to show it.

I've developed an example here https://github.com/texano00/ionic3-dialogflow-webdemo-example

2. The right way

I've called "The right way" because this way uses the official Dialogflow client API in order to integrate the chatbot.

Now, instead of having a web view in an iframe, we have the total control of the UI.

So, let's go to an example:

First of all install the library npm i api-ai-javascript

Here, the full working example using the offical Dialogflow API https://github.com/texano00/ionic3-dialogflow-client-example