I am currently working on a language overhaul for D&D. Simply, I hate the way languages are done, normally, and especially that "common" does not refer to anything, actually. So, no more! At least insofar as my own worlds. The other DMs may do as they please.
There are two types of languages: innate, and learned. Innate languages are those which are natural to a certain specific folktype, and don't have real-life phonetic and/or alphabetic equivalents (for example, trilling, purring, or even telepathy). Learned languages are those that can/are taught to be spoken and written. One can learn another folktype's innate language, but they will have some difficulty expressing themselves with full clarity since they likely will not be physically capable of mimicking the sounds or body language required (e.g., if a tail needs moving, or ears flicking, etc.).
Special shout-out to Zach for making his folktypes share a name with their home territories. Makes overhauling in Kimarui that much easier.