In the Classic version of zendesk Live Chat you have API method zE('webWidget:on', 'chat:unreadMessages', function(number<int>) {}); which gives possibility to react on receiving new messages.
We want to switch to a new Live Chat and some of these methods are really needed for us. I am trying to achieve the same behavior with our own hooks, but it is really hard to track appearing iframes as they have only titles as identifiers, which can be translated depending on user locale.
So my question is, is it possible to add some sort of ids to iframes?
Or there are any other workarounds how to achieve the same behavior as classic chat has? 
Thanks for posting your question to the Community! Unfortunately, there isn't a way to add ids to the iframe. Just to clarify though, when you say new live chat are you referring to Messaging?
Also, if you're able to provide me with a bit more context about what you're trying achieve by tracking appearing iframes, then I may be able to help come up with a solution. Hope to hear back from you soon!
Best,
Erica