Ax has mentioned a few times that to Andalites, a book is more technologically advanced than the computer. I've recently been trying to figure out how a species could develop in such a way that they completely bypass the book altogether. I guess since they probably aren't cutting down trees or using any other sort of plant material to manufacture things, they wouldn't have our idea of books. But if they were able to make computers, then certainly they could have gotten suitable material somewhere. So I've got to think that the only reason they never did is because the idea of writing symbols on paper never occured to them.
With what is essentially telepathy as a communication method, it seems like Andalites wouldn't have developed the concept of a word at all. Before they made first contact, all they had in terms of communication was other people's thoughts, so thought-speak would simply be concepts instead of actual words. Once they started making contact with other alien races, the idea of words became a part of thought-speak, but at a point in their civilization where everything was run by computers. But this is all theorycraft.
This is kind of all over the place, so I'll just ask: Is there ever a reference made to Andalites having any written language of their own? I don't recall any being made, but of course that doesn't mean it didn't happen. The closest thing I could find was in The Arrival (38), where Mr. King hacks the Andalite computer for Ax. The only references made to output are the computer requesting a code in thought-speak, and "Counters appeared. Images scrolled past in a blur." The rest was translated by Mr. King.