Looks like the cultist language from Lovecraft's original "The Call of Cthulhu". As far as I can recall, only the phrase ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn ("in his house at R'lyeh, dead Cthulhu waits dreaming") actually appeared in that story, but I have no doubt the many authors and fans who have expanded the Cthulhu Mythos over the decades have extrapolated on it...
