Although I do not know if Mr Russell took a view on speaking in tongues, I would agree that you have correctly interpreted the effect that such a form of 'prayer' or meditation would have on the mind. In shutting out the rational noise of thought, "knowing everything" (as you say) or enlightenment can then be revealed through listening to nature (to use Mr Russell's terms); I have included a brief description of 'Siddharta' by Herman Hesse (snagged from wikipedia) which brings to mind this concept of excluding the rational mind to allow the universal mind to flow into our awareness:

"Siddhartha's friend of his youth, Govinda, comes by the river, still a Buddhist monk and still searching for enlightenment. When he asks about the teachings that have brought Siddhartha peace, Siddhartha replies that too much searching can preclude finding, that time is an illusion, that all things are one, and that love for all things is the most important thing in the world.
Then Siddhartha asks his still skeptical friend to kiss him on the forehead. After complying, Govinda no longer sees his friend Siddhartha, but rather a sea of people, animals, plants, and other objects of the world. Thus, Govinda discovers the oneness of the universe, just as Gotama, Vasudeva, and Siddhartha had before him. Govinda realizes the perfect truth of Siddhartha's wisdom, and, weeping with wonder, bows down before him."