Aight time to speculate, i bet harpies will have the most flexible and advanced language, as bird type monsters if we consider their parallels with real life birds, the encompass body language, color, sound with songs and signals, and they even have tool use, that covers practically all the variations so far, which means Harpies should be in theory great translators and communicators with smell being their downside, however i wonder what their particular version of communication entitles? i bet they will use songs.