I know the idea of language being magic is not new- heck, it goes back to the bible being the Word, and I'm sure beyond that. And I'm sure some of you might give me examples of this very idea: magic being the use of a older, more primal language. But I want to think a little about what the implications might be.
So, what if spells were just sentences in the right language? The language of the long lost elders? You would need to find examples of that lost language: inscriptions, scrolls, books. Even second-hand citations might be valuable.
You might find a book written in that tongue and use it to reverse engineer things: nouns, verbs, sentence structure. What you could do would be very limited and simple. Saying the word for light would create light.
You might find a dictionary written in the old tongue. Now it is more clear what the names of things are. Perhaps with its help you can learn more verbs too. You can affect more things now. When you say flee, foes flee. When you say "light flee" light sources are extinguished.
You might find a grammar book, or rhetoric. Now you can learn the structure of the language to make more complicated utterances. You can have multiple effects happen to multiple things. You can include contingencies and qualifications. "Take me to safety." Or maybe: "Make the tracks of he who wishes me harm visible to me."
With a magic system based on this concept, all spell effects would essentially require some research. Well, unless that's what guilds are, the accumulated, simple knowledge. But leveling would be based on treasure. Because to learn how to do more complex things would require the finding of the books in the old tongue, the grammars, etc. This might be a kind of individualized achievement based leveling for magic-users.
That all being said, the more I write about it the less different this seems than the way the game is set up now: spells being kinds of arcane "recipes," and guilds being centers of recipe knowledge, and magic-users hunting the wilderness for lost and rare recipes. Hmm. . .