Since it's from an anonymous author I highly doubt the book is protected by copyright. Wanting to copyright it would have required the author to submit an application or something with his legal name.
I think once the translation is complete someone should copyright it before releasing it on kindle and mention that it was written by an anonymous author to try and give him credit that way.
Actually, as soon as anybody has written a work (or recorded a song, taped a movie, etc.), that work is under copyright to them. I know this is the case, legally, in at least the US and UK and most other countries. Registering the copyright simply makes it easier legally to defend against cases of copyright infringement--without registering the copyright, one has to provide evidence (previous drafts, etc) that they are the original writer in case of a legal dispute.
Copyright still holds even in the case of work by an anonymous author, but the length of the copyright changes. Usually, the copyright lasts for a shorter time (anywhere from 50 to 90 years from date of publication depending on the country), unless the author comes forward in which case the duration of the copyright usually reverts to the normal, longer length.
Translations of a work require the consent of the original copyright owner.
Now, this is where it gets murky, since I have no idea what the laws or protocol are for translation of a work by an anonymous author. However, since it seems the author didn't really expect much (if any) monetary compensation from the work, and since the author's intent was to spread the idea more than anything else, and since it's doubtful the author would want to come forward, I guess from a moral standpoint, it would be okay to distribute a translation.