Bow Down To Nul/The Interpreter by Brian W. Aldiss
Brian Aldiss is often closely associated with the British New Wave of science fiction authors from the mid-1960's. This short novel, first published in 1960, remains in the tradition of alien fiction that was popularized in the 1950's.
Far in the future, the alien race of nuls from the planet Partussy have established a galactic empire streching across thousands of planets. On Earth, a remote outpost, the High Commissioner is abusing his powers by mistreating humans and skimming profits from the giant tree farms. When the Partussian Lords hear of this they dispatch Signatory Synvoret to investigate. The earthman Gary Fowler is Chief Interpreter for the nuls and also playing a secret role as spy for Rivars, the rebel leader. When the alien Synvoret arrives on Earth it sets off a chain of events that change things for everyone!!
Obviously, Aldiss was influenced by the British Imperialist experience and yet when you get down to it this novel is just a cool character study. It was a good short read but I don't suggest you run out and buy this one.