Quite so, but upon reflection, are the Chasch, Wankh, Dirdir, and Pnume really that comprehensible? In each case, they use specially adapted human intermediaries to communicate and deal with humans. As predators, the Dirdir are the most understandable by analogy with terrestrial grassland hunters. But in essentially all cases, it is impossible for "raw" humans to communicate with these races - and this is Vance's exceptional work featuring alien races, forcing him to compromise to a degree in order to produce a successful story. I believe that Tschai is the exception that proves the rule.