I'm not a native Spanish speaker but I know the language well enough to be disappointed in the translation of the title of The God Delusion. Admittedly, "delusion" seems to be a difficult word to translate into Spanish and the book is known as "El Espejismo de Dios".

An "espejismo" is something like a mirage or an optical illusion, which is not quite the same thing.

Perhaps a native Spanish speaker could comment on this.

Yes indeed. A native Spanish speaker friend of mine comments as follows:

There is a problem with the title, because "espejismo" literally is 'mirage', and while is fine for the title, it makes nonsense of your reference to a delusion by an individual being a psychiatric issue. They use espejismo everywhere you use delusion but leave the rest unaltered, so that they say for instance that the dictionary definition for espejismo is…and then they translate literally what you said is the definition of delusion. Anybody can see that what you are then saying is wrong.

This is beyond incompetent translation, it is downright stupidity.