It is my experience that there are generally three schools of thought on languages in RPGs.
School 1: D&D Vanilla-ism
Codified languages based thoroughly on race and boxed for convenience by the rules of the game from setting to setting, varying only slightly. Examples: Common, Elf, Dwarf, etc. Detailed, but without detail.
School 2: Who Cares
Some groups could care less who speaks what, they just don't really give a thought to it. They want hacks, slashes, loot, and survival.
School 3: Details, Details
Here's where I fit. My game world is defined in part by its languages. I don't want it to be terribly easy for the PCs to communicate with someone else from a different nation. I want language barriers to reinforce that it is a fantasy world that changes with the actions of the party and others. Should all the PCs instantly speak something so bland-sounding as Common? No - but they'll probably speak Karthaginian, since it's the most widespread empire on the map. There are probably going to be individual languages found within that same empire, as well, since it stretches so far. The folks in Megiddo speak Megiddian, there's the dead language that was once spoken by the Voori (Vooric), and perhaps local dialects of Karthaginian spoken in Antioch, Pergamon, or Pangkot. Just within the area south of one of the main bodies of water in my game world, you have the following: Xotathi, Phyrgilian, Lengite, Kombolo, Kongese, Uccastrogi, Aktenshepolite, Seljuk, Kanaima, Ongian, Yezidee, Haemodite, and Khapuran.
And then I get the urge to do something really weird - well, it is sword & sorcery/sandal/weird/pulp fantasy-influenced, right? Here are a few I just dreamed up - not sure what, if any, game mechanics are going to be involved, but I'm going to work some of this into the magical background of the game.
Black Speech: A tool for evil beings, sorcerers, and priests of dark gods. Strangely, it can enhance the efficacy of evil magic (that is, magic used for evil purposes), but also opens psychic doorways to things that lurk in the Outer Dark, influences that can creep into the psyche and possess the speaker.
Red Speech: The secret language of vampires, hidden from mortal eyes at all costs. Even learning this language can bring strange urges to mortal minds.
White Speech: The language used by the priests of the Nameless God of Megiddo, the only pure and benevolent god in all the lands. It is used to cancel any effects of the Black Speech, and for divine rituals.
Vooric: A dead language, once spoken by the extinct Voori people, but preserved through the undead speakers that still exist within the Necropolis of Voor. It has a pictographic alphabet, and it is necessary to understand many of the rites of the Voori practiced in the mountains depths.