johnomarkid

No frameworks, no boilerplate - this is a great idea. I've seen too many junior developers go straight into learning React/Redux, or using bootstrap, or plugging in some library like velocity.js. It's often easier, more efficient, and more maintainable to use plain javascript with web APIs.

A slack clone using firebase as a back end could touch on a lot of topics that would help you learn react inside and out - components, state management, routing, interacting with a server (ie firebase, but avoid the firebase-react library so you can architect things yourself) and more.

I've lived in Berlin for 3 years and have never had to use German to interact with people in the startup community. Since a high number of startup founders/employees are from other european countries, it's more practical to use English as the language of business.