At the moment, WhatsApp does not have an interface that we can interact with, to allow us to properly listen for new messages or reply to messages.
We have asked them, as you can see below:
Message sent to WhatsApp support on April 29, 2016:
We are developers on an application that reads messages out to users. At the moment, We support Hangouts, SMS messages, Gmail, and various email clients. Our app basically allows my users to hear their incoming messages instead of reading them on their device. For Gmail and SMS messages, we can also reply, using voice recognition. This, as you can imagine, is quite useful to my users, specially those that have a vision impairment, etc.
We were wondering if there was a way for us to programmatically access messages so we could read them aloud to our users. In addition, a way to programmatically send messages too would be super useful. We look forward to hearing back from you.
Message received from WhatsApp support on April 29, 2016:
##- WhatsApp Support -##So, at the moment, there isn't much that we can do. However, maybe if more of you ask, they will consider it more strongly!?!
Thanks for your message.
Unfortunately, that is not supported at the moment. We are always working to improve our app and will take your suggestion into consideration.
If you have any other questions or concerns, please feel free to contact us. We would be happy to help!
WhatsApp Support Team
You can still have partial support using our "Other Apps" notification reader. Using this feature will allow you to at least be notified of your incoming messages. Dont forget that once you enable WhatsApp in our "Other Apps" reader, that you may have to customize the text, to read out the bits that you care about.
If you need more information, please let us know!