I wanted to agree with this, but this line (mentioned as a premature optimization) is absolutely baffling to me: “More than one language for your application.

I wanted to agree with this, but this line (mentioned as a premature optimization) is absolutely baffling to me: “More than one language for your application. For example, a backend in Golang, Ruby, PHP etc. and a Frontend Web App in React, Vue etc.” When would your front end and backend ever be in the same language? I guess JavaScript would be your only option?