Confluent only officially supports the Java client (and now has a Python, Go and .Net clients as well that I didn't know) and it is really recommended to use the client with the same version of broker due to protocol incompatibilities.
Most Kafka client implementations are open-source projects of their own, this is also true for most redis clients implementations, but again: Kafka protocol is much more complicated than Redis.
I haven't used Kafka with other languages besides Java or Scala, so I can't really say how mature are the other clients.
But my point about how easy is to implement a client for Redis if needed is still valid. =)
As someone who has been burned by non-Java Kafka drivers, beware the perception of ecosystem support here. The Kafka design pushes a huge amount of complexity onto the client, and in our experience only the Java client deals with this complexity well. We started out using Python clients but eventually moved to Confluent's REST API (wrapping the Java driver) because we had so many problems with it.
Most Kafka client implementations are open-source projects of their own, this is also true for most redis clients implementations, but again: Kafka protocol is much more complicated than Redis.
I haven't used Kafka with other languages besides Java or Scala, so I can't really say how mature are the other clients.
But my point about how easy is to implement a client for Redis if needed is still valid. =)