I like the idea of introducing language into the game, but I think the idea of diplomatic or trading restraints for civs with differing languages is a bit much. I almost think that you could separate languages into families instead of specific language themselves (Slavic, classical, Latinate, Anglo-Saxon, Native American, Sumerian or ancient Persian, Semitic, Asiatic, ect.). Each family could have its own wonder to spread its influence (like
The Odyssey for classical or
Beowulf for Anglo-Saxon)-- these monuments could even be used to found them in the first place. Languages could work like religions in the sense that they incur positive or negative diplomatic points and influence espionage points.
In conjunction to language families there should another tier in the civic options. They should come in effect as a civ progresses in the tech tree. These can provide bonuses to culture, science, religion, espionage, research, commerce, probably anything you can think of. Here's my own idea:
Tribal Ritualism (or something like that): low cost, no effects (or small culture boost), Starting Civic
Commercial Exchange: low cost, trade/science bonus for cities with state lang.,spread culture in cities connected to trade route, spread state lang., Req. writing
Monasticism: Medium cost, no non-state lang. spread in cities w/ state rel., science boost to state religious buildings, missionaries -15% production cost, Req. Theology
Censorship: high cost, no non-spread culture spread in cities, +5-10% maintenance cost, +15% espionage points in all cities, Req. Court of Laws
State Propaganda: high cost, -15% war weariness, -15% Civic maintenance, -2 w/ all leaders, Req. Facism
Free Press: low cost, university +

, +35% research in all cities, Req. Liberalism
Globalism: medium cost, +

and culture for each language in city, + culture per religious building, +10 research, +2 w/ all leaders.