Indeed, thanks for correcting.Sumerian & Akkadian are two completely separate languages. Yes they did affect one another a lot, but they're very different languages. Akkadian was Semitic, Sumerian was not.
Aren't all languages originally languages of the masses? In Akkadian though you do find 'litterary Akkadian' with its own grammatical/morphological fatures, and even 'standard Akkadian', just like Classical Arabic, MSA and the dialects.They were both originally languages of the masses. Each was adopted as a lingua franca, by non-native speakers, just as Aramaic was, and also as Arabic later was.
By the way, my point (which I realise was not explicit) was that Arabic could have followed the same pattern.
I raised two other points that would suggest the contrary because, as I said, I'm only thinking aloud here, and I'm not favouring any conclusion because there is nothing 'at stake' for me...