My German editor was kind enough to contact me after seeing this website in order to cast some light on the reasons why the name of SOMETHING MISSING was changed in Germany. I'm posting a portion of her email here, with her permission:
You mention that SOMETHING MISSING apparently doesn't translate well into German; it indeed doesn't - it would have had a rather negative connotation if we'd translated it literally - but there is more to it. In Germany we have a law, Titelschutz (Title Protection) that states that one title (be it a book, movie or whatever) must not resemble another.
So a person who goes into a book shop and says "I'd like to have this and that" must be certain to receive the book he or she is looking for and not a different one which only happens to sound alike. A title like "Etwas fehlt" or "Fehlt etwas" would have been too close to titles which have already been published. THE GOOD THIEF wasn't the most innovative of all titles but it sticks in one's ear and is unmistakable.
This rule causes quite a few problems in general by the way, since the number of combinations of words is, well, limited. At least the number of meaningful combinations.
Interesting, huh? It's been hard enough trying to find a good title for MILO. I cannot imagine having to also worry about using a title that is too close to a book published fifty years ago.
She was also kind enough to send along the cover art of the German version of the book, which I like a lot.