Xyor, a wizard, spoke to Rezyl Azzir in Legends and Mysteries: Rezyl Azzir. It sounds like her words were somehow translated from whatever language she normally speaks in to human languages, but it was painful for Rezyl to listen to her speak.
Rezyl flinched as the wicked woman began to speak in a tongue that resembled torture more than language.
The pain was searing, complete.
The demon approached the writhing hero.
As she spoke her violent words began to take shape, morphing from syllables of death to a known offering of haunted human languages.
The demon woman leaned in close… and whispered, intimately.
Rezyl’s ears bled as she spoke.
Toland apparently spoke to Ir Yût, the Deathsinger, in Ghost Fragment: The Hellmouth but it’s not mentioned which language she spoke in. Oryx also spoke to our guardians in English in the TTK campaign, but it’s not clear if that was due to his words being translated, perhaps by our guardian’s ghost, or if he had learned how to speak English.
We haven’t encountered Savathun yet, so we don’t know if she can speak English. Perhaps you could have her speaking in the hive language but her words are translated into English by a ghost? Or you could do something similar to what happened with Xyor, where her words were somehow translated into human languages even though Rezyl’s ghost wasn’t present.