There is more than one opinion on this matter. For example:
Rabbi Joseph B. Soloveitchik famously wrote GOD on a blackboard and erased it in front of a class to make it clear that it was not a "shem" when it is not Hebrew. I have read this numerous places but you can find it referenced here.
That being said, it could be seen as more respectful to write G-d, especially when the book may be read by people who follow a more stringent opinion. An author would free the reader from having to consider the book shemot. For example, I was dismayed when reading "Boychicks in the Hood" to suddenly come across the four letters of the divine name in Hebrew in the center of one page. It causes mental anguish. Did I read it in the bathroom before I knew its status? What if one of the kids threw it on the floor? Why should the author cause these problems?