Childrens Book, 90s or earlier; Story follows multiple characters, one of them is a young girl who gets turned into an animatronic parrot, other children "disappear" in similar ways. Read in late 1990s (German).

[Sirence]

The girl is not the main character, I believe a man was. The girl can not talk after being turned into a parrot. She can only say one word which is her name, but I can not recall the name. It might have been a short name, maybe starting with the letter 'N'.

The book had a lot of tear when I read it in the late 90s so it might have been older.
I read the book in German (Bavaria), however that might have been a translation.

Sadly I can not recall the main plot of the book or any other details.

Spoiler: The girl starts to forget she used to be a girl as the story progresses. The main character cares for her and I believe adopts her in the end after the story is resolved.

[Sirence]

After some more digging I believe the book might be
"Die Reise in den Sternenhimmel" by Petr Chudožilov.

There is absolutely zero information about the book online except for images of the cover and the back, where instead of any details about the plot the first page of the book is printed. It was published 1992. Apparently it is translated from Czech, however not even the original Czech title can be found anywhere, not even on the authors Czech Wikipedia page.

But I do recognize the cover and I clearly remember owning it some time in the late 90s although I can no longer find it, so I can not confirm it's the book I am looking for but the possibility is high.
If anyone has this book please let me know if there is a plot line like the one I mentioned in the first comment.