Maybe an empty string or 0x007F?
http://msdn.microsoft.com/en-us/libr...fo(vs.71).aspx
By the way, I only have an English dictionary installed (the GNU dictionary), but when I look a word up from a French book (language set with mobi2mobi) it still tries to search the dictionary (and returns no result), I mean it does not complain about no dictionary existing for the language...