Wow, I wonder, no replies. Now steemit is too full and it becomes fuller every minute. Concerning what about to write and to whom- if you see your writing as kind of diary, than you don't have that problem. By writing you get the things you are interestet in clear for youself in the first place.
With so many different languages on hand, I can imagine how difficult it is to make a decision. It is strange sometimes I am avoiding writing in my mother tongue, but don't ask me why. Esperanto ĉi tie estas kiel ludo kaj praktikado. And English for fun and socializing.
Writing a whole book. Why?
People are different, don't bother -you are complete OK!