Common is the official language of humans, but is readily accepted by most races and civilisations. At its simplest, Common is an amalgam of Dwarven, Elven and idioms from other languages, all of which have been homogenised into a phonetically consistent tongue.
As the language of the Dwarves, Dwarven is a thickly-accented language of hard consonants and an expansive vocabulary. It possesses a harsh and utilitarian sound, employing a variety of nouns and verbs built to precisely describe a variety of situations. Words in Dwarven tend to construct off each other; if "arau" is large and "glor" is lake, then the ocean is "arauglor." The Dwarven script is derived from Giant runes discovered deep underground; as such, Dwarven runes and speech retain some measure of magical power.
Elven is the Elve’s tongue, and is an elegant, flowing language with an almost musical quality. It is derived from ancient Sylvan, with unique dialects for every subspecies of Elves. Elven sounds like poetry and looks like calligraphy, and complex thoughts and feelings can often be expressed with a few simple, well-chosen phrases.
Gnomish is an odd, somewhat stilted language that sounds silly to many non-native races, reminiscent of the Gnome’s proclivity towards whimsy. In reality, Gnomish is a distant descendent of Sylvan and Giant, with a sing-songy tone and a high degree of precision. As opposed to Dwarven, which combined existing words to represent new concepts, Gnomish boasts an enormous vocabulary of unique words for a variety of specific situations, forcing any non-native to learn an immense number of vocabulary words that differ by region.
The Draconic language is a harsh, sibilant language primarily spoken by dragons, Dragonborn, and other reptile-adjacent creatures. Though unable to be spoken by most humanoids, the Draconic script has been used for centuries as a semi-official language of arcane notation and spellcraft, often taught in wizarding schools but rarely used as a verbal language.
A derivative of Giant, Orc is a harsh, rough-sounding language specific to the orcish tribes. Many confuse the language with Goblin, and the two languages do indeed share some overlap in their history. As orcs tend to hold a fierce oral tradition, there is very little in the way of orcish texts; however, some native scholars have found workarounds to preserve stories, discoveries, and laws. They use either a scratchy cuneiform-like text or the Dwarven alphabet to represent their sounds, though the translation loses a significant amount of meaning without vocal cues and inflection.
Goblin is a stern, barking language with roots in Draconic. The language is built to convey imperatives as efficiently as possible, and is consequently used as a language of authority in societies with notable goblinoid populations. The language is spoken most articulately by hobgoblins, who adhere to the careful grammar of Old Goblin no matter where they might be stationed. Bugbears and goblins are more likely to branch off and create dialects peculiar to their region, often drawing words from the native tongue to create mixed languages that more easily convey civilian concepts.
Undercommon has faint roots in ancient Elven, Dwarven, and Deep Speech, as drow, duergar, and the occasional aberrant society were influential in its early development. It bears no relationship to Common except for its initial purpose--to serve as a trade language between a variety of coexisting species in the Underdark. As it is mostly spoken in regions of near-total darkness,the resulting language is a strange mishmash with a heavy focus on volume, vibration, and resonance - carrying more information and intention in its delivery than languages spoken in the light, where non-verbal cues do much of the heavy lifting.
Giant is one of the oldest languages in the world, full of deep, vibrating tones that most medium-sized humanoids find impossible to replicate. Though spoken by many large creatures such as trolls, ogres, and firbolgs, these versions of the language lack the inherent magical power of their ancient progenitor. When spoken by the massive lungs and vocal cords of true giants, the language takes on an inherently magical quality reminiscent of Primordial.
Derived from Primordial, the Giants perfected the art of runes to create the most powerful pictographic language of all. With the Giants largely extinct in the modern era, these runes now only survive in their Dwarven descendants or in deep, well-hidden caves ruins that serve as time capsules of the ancient Giant empire.