It would definitely take some work, but I think implementing languages could be done if conversations were done as a party. For example, if you have one or more people in your party composition that speaks the language, then you as the player will also be treated as if you understand the language. Even if "everyone" speaks Common, you could probably implement languages by having books/scrolls that could only be read if you have the language. For example, I could see a scenario where the PCs kill an evil drow wizard, but unless someone speaks Elven, the wizard cannot copy spells from the spellbook. I could also see puzzles (like the door to Moria in Lord of the Rings) where you have to know the language to succeed or continue.
The point is, even if everyone "speaks" common, Larian Studios can still implement languages in written texts and in other ways.
