Considering their ability to cast spells it is quite possible the Aranea are capable of speech, though I always imagined they chose not to talk because of their high pitched, chirpy, happy sounding voices. Did the Aranea queen in Nethergate have a high pitched voice? I can't remember. Also was it sort of implied the GIFTs in Avernum did in fact originally come from the world of Nethergate? It's been a while since I played and I can't recall the GIFTs origin story all that well.