This repo contains a protocol buffer, for a customer service, as defined in the Medium article. This single protocol buffer has then been implemented in 4 different languages:
Each of these languages has a client and server implementation (with the exception of PHP which just has a client). The implementations all use generated client/server libraries from the (protoc)[https://github.com/google/protobuf] tool.
See the README in each language folder for more information.
Hint: Yeah you could be dull and run the client and server in the same language. But you don't have to! The magic of protocol buffers means the client/server implementation doesn't matter. It just works.