Language tends to get one of two treatments in fantasy — either it's never looked at, everyone speaks English and it's all fine, or Tolkien. Mr T being a professor of Anglo-Saxon, I think, he went to town on the languages in a big way. Indeed I believe I read that the languages came first, the history second, the actual fiction some time later. Few writers have the time, fewer still the formidable scholarship to emulate, but there are a fair number of fantasy worlds where it is at least acknowledged that the elves speak elvish, although for ease of reference everyone except the humans seems to be effortlessly polyglot. The Fellowship of the Ring would have been extremely different without a common language between them, after all (1).
In the world of the Insect-kinden, all the kinden share a language (2). There is, however, a Reason for this. It's not just that I couldn't be bothered, honest. However, I'm feeling perverse enough not to simply explain, so I will content myself by pointing out that this remarkable commonality of language has not gone unnoticed by the clever men and women of the Great College. To give you an indication of their current thoughts on the subject, I have swiped an itinerary from one of their conferences, which I present for your delectation here.
For reference, this conference is taking place somewhere around the same time as book 5, which is actually important. The keen-eyed may wish to speculate on the import of some of the lesser items in the schedule too…
(1) The film The Thirteenth Warrior at least acknowledges this problem, with the arabic hero having to work hard to pick up the speech of the vikings he ends up accompanying, after an unpromising start where his servant manages very basic speech using mangled latin and greek. Whether you go for the linguistic montage the film lands us with, at least it admits to language as a barrier. (In Crichton's original book, Eaters of the Dead, the hero never really does learn the language, but gets by because one of the vikings speaks latin.)
(2) This isn't English, of course, but your humble author has kindly translated.