glossolalia is not linguistic and that xenoglossia is unconfirmed. I had thought that glossolalia had more linguistic structure than it appears to have. On the other hand, SM Stirling's Emberverse is part of a narrative where divine apparitions and related phenomena demonstrably occur so maybe it does make sense that the High King has this linguistic gift?
The opposite effect, the confounding of tongues, is prominent in the story of the Tower of Babel and, following that, in Volume III of CS Lewis' Ransom Trilogy:
"'Qui Verbum Dei contempserunt, eis auferetur etiam verbum hominis.'
"They that have despised the word of God, from them shall the word of man also be taken away."
-CS Lewis, That Hideous Strength IN Lewis, The Cosmic Trilogy (London, 1990), pp. 349-753 AT Chapter 16, p. 718.
Lewis' contributions and commentaries deserve wider recognition.