The most important form of language and communication in Libation Bearers is communication between the living and the dead. Wait, scratch that. What's most important is the attempted communication between the living and the dead. Let's not forget that the play is called Libation Bearers, after all – a reference to the ritual offerings mortals would make to the spirits of the departed. Amazingly, the scenes of Orestes and Electra's respective offerings to the tomb of Agamemnon, plus their set-piece song sung together with the Chorus take up about 1/3 of the play's total length. Most of what's going on there involves the good guys' praying to the spirit of Agamemnon to listen to them, and to give Orestes the strength to carry out his revenge. If it's really true that the living can communicate with the dead, what effect does that have on the overall notion of revenge? What if the dead are unreachable?
Libation Bearers gives no sign that communication is possible between the living and the dead.
Clytemnestra's words to Orestes make him change his mind about her – but only after it's too late.