I can see how there could be some overlap in content on the two sites.
What does this site focus on, and what is disallowed and should be asked on the English site instead?
This site focuses on writing style and technique, questions about editing, publishing, finding an agent, etc. Anything involved with the process of writing a book (or something else) to getting it accepted by a publisher is within our realm.
This site disallows grammar questions, and any language-specific question. It disallows questions about the subject matter about which you're writing. It disallows questions about getting illustrations.
We are not limited to creative writing; poetry, playwriting, and nonfiction are also within our realm of expertise.
Honestly, I don't see its similarities to English other than that it happens to be conducted in English.