On the subject of the language of magic, here's a story:
What if originally magic were something different? A primal magic based not on communication, words, phrases, etc, as those things did not exist in those times. First there was nothing. Then from the nothing came the first wills. These wills were aloof, apart from matter and even such things as life and death. Yet as time passed, these wills constructed concepts in their ponderings, concepts that gave rise to thought. This is where Psionics comes from - it is the power of will alone.
These concept evolved and grew until came the concept of that which belonged to a will and that which was without. And so came into existence the separation between substance and mind. This is where Science comes from, the rules delineating the behavior of substance absent will.
Now from substance grew mockeries of the true wills of the universe - things of clay that lived and died, and thought small, isolated thoughts. The necessities of their existence, of life and death, passion and sorrow, gave rise to a new mode of being, that of emotion, or irrationality. It was a thought that was not thought as the ur-wills knew, and it had power in its own right, for it lent one strength to deny the bonds of substance in times of need or desire, to grasp a bit of that power that was held by those who envisioned the cosmos. Yet this wild power was uncontrolled, chaotic, and destructive. This was primal magic, the magic used innately by supernatural creatures.
There came a time when these early beings developed the means to communicate, to take their feelings and surround them in a bottle of words, so that they might be transmitted to each-other without the direct contact of minds that was the purview of the psions. And so words became a new vehicle, a new form of life, but one that was hollow without those who spoke them. As thoughts and emotions were linked to words, a melding occured between psionics and primal magic, the creation of something new, something whose power was that of context. This is arcane magic, and the language of magic has evolved ever-since.
There is no one magical language, because for words while grammar gives structure, context is king. The training a wizard undergoes creates a set of links between the magical language they learn and the thoughts and emotions of their mind. These links lie deep below the surface of the wizard's consciousness, and tap into primal aspects of their being that have long-since been dormant. Study of magic opens up more possibilities, makes more links, and so the practitioner becomes able to create an increasing variety of effects. The study of another wizard's spellbook is the establishment of translation between one's own concept map and that of the author's, and so it is never an easy matter. Scrolls are words that have had their concepts bound into them, given small wills of their own - a wizard who studies a scroll to learn a spell allows those words to write themselves into their mental library.
If one makes a study of magic across many prime material worlds, one finds a hierarchy of these magical languages. It is possible to trace the evolution of the language of magic back in time, looking for places where the lexicons have small variations from eachother and reconstructing dead versions. This study leads one back to an ancient progenitor tongue, one that has wormed its way into every corner of the cosmos. Even more significantly, it is a language which every immortal supernatural creature is familiar with at some level, something from the times of their origins. And so it can bind them, its words recalling memories of that distant past. One who learns the intricacies of this lost language can bind and command such creatures, even to the point of influencing the first wills whose thoughts comprise the cosmos. This is true speech.
Divine magic is much simpler, and is somewhat newer in nature. With the development of wills made of substance, a vast number of wills were introduced to a cosmos that had previously known only a few. The thoughts of these wills were weak compared to the first ones, but they made up for that in number. With time, the power of these thoughts collected in commonalities, things that everyone at some level believed in. With time, people made their own names for these ideas, and thought of them as entities in their own right. And thus were born the gods and spirits. Divine casters tap into their power by establishing a relationship with them, and then using their own belief as a conduit. The words of divine spells are not part of a magical language, they are simply rituals of the caster's religion, things to focus their belief. Divine scrolls are different than arcane scrolls - their power is not that of words with a will of their own, but is instead contained within the ritual significance of the object. A divine scroll is made by performing the proper blessings and rituals. What the scroll says is established by the traditions of the deity it calls upon, but does not bear the scroll's actual function. This is why divine casters do not (generally) learn from scrolls - the blessed object has power, but the ritual text does not have meaning to a believer in a different deity.
