My first thought is that no edition of D&D has handled language realistically (for all "realiistically" is worth in a fantasy game). If you're not going to have a common tongue(s), you'll want to enable characters to speak multiple languagues to varying degrees of ability, or add in some trade pidgins, which are kind of like a common tongue but typically limited in the topics you can express. I agree that racial languages are not as good as regional/cultural languages. And the idea of prestige level is cool. Upper-class folk literally don't speak the language of their servants, and lower-class folk can understand upper-class language, but somehow never master the nuances that signal one as a member of a particular class.Having a lot of trouble getting the Deities out of my head, individually, so I thought I'd touch on something else important:
Regional Languages feels like a really strong direction to go with it, rather than having a dozen different racial languages tied to specific groups that are spread across the world in a disparate way. But by the same token that can make it difficult for a specific group of people to have a signifier of at least quasi-unity.
So my current thought is to do both regular languages and also some sort of sublanguages? Like High and Low languages in the wake of the Norman conquest of Britain in 1066, where French became the primary language of the upper classes while the lower classes were still largely speaking English but with some word-filtering (pork, beef, poultry, venison, and other meat-related words, for example)
I'm pretty sure I don't want a "Common" tongue shared by everyone... but if we do have one, I think it should be the language of the Ancais, showing off their massive cross-cultural impact in the wake of the Age of Swords. Though, honestly, we could go all "Norman Invasion" and make Acain the dominant "Noble Tongue" across Annam, Musarra, Kyran, Myr, and Gresia... And then have Ellenici be the common tongue between Ellenici and Neasc. But that kind of singles Imba out and I'd feel really weird about that. Though it could reinforce the "We were never conquered" angle.
What are your thoughts?
That's all for people who dig that kind of roleplaying, though. Careful not to alienate the people who just want to swing an axe!