Song and Steel
In an attempt to classify the tremendous diversity of languages on our world, most scholars begin by dividing the languages into two primary groups consisting of humanoid and insectoid languages. The humanoid-dominated scholarly work tends to refer to these language groups as Common and Entomon, although Entomon is often referred to as More Common by the general public.
Of all the proposed reasons I have seen for the Common/Entomon division, the most compelling is that most native speakers of one of these categories of language will rarely have the physical capabilities of speaking a language from the other category. As an example, a human has the physical capacity to produce most if not all sounds needed to speak elven, but that same human does not have the mandibles, claws, wings, and pheromone glands necessary to speak formian. There are many exceptions to this rule, but it is the simplest concept I have seen thus far for organizing the myriad languages the average student may encounter.
I would like language to play more of an aspect within the campaign to add an extra element of immersion without becoming needlessly hindering. Having a “common” language that practically all races speak is certainly an easy fix for gameplay purposes, but I feel it often leaves races underdeveloped with the feeling that they’re simply humans with some quirk. I feel the main goal of a diverse and blended array of languages for the game world would be to make the players feel like they are one among many; the world has a tremendous amount of cultures and consciousnesses that exist in drastically different ways. Considering a particular race’s language really helps me to get a feel for how they might behave, so it’s mostly a tool for me to help stretch my imagination.
Mechanically, I would like to experiment with a point-buy type of system for language acquisition. It would likely involve attaining some variable level of competency in the language based on how many points you invested in it. The amount of points a character has to spend on language proficiencies would likely depend on their intelligence, wisdom, and charisma scores, and greater proficiency within a language would give bonuses when dealing with its use. Toying with this is fairly low priority.