I have a fantasy story in my head for several years now. I wrote an outline for a book and draw a crude map of the world. I even started writing the first draft, but one of my biggest problems is my vocabulary. I am Swiss and my native language is German. But I mostly read English high fantasy (Tolkien, Howard, Sanderson, Eriksson) and also watch movies in English. But still I am struggling to write something that doesn't feel it's written like a primary school essay of an English or American child. I don't like reading and writing in German (I blame my German teacher), the only exception was the Witcher books as the German translation from the original Polish ought to be way better than the English.
Is there a way to get more (fancy) words in to my vocabulary to make it a better read, beside the aforementioned reading and watching in English?
Or, probably too opinion based, does it even make sense to try to write a novel in a non native language?