Any specific language that belongs to a race (like zebra's special glow-language) still exists and is used in Flameverse, but this page is mostly for regional languages spoken by all races.
Note that all races, after they are born, gain something called "common knowledge". This includes how to speak the language called Common and read basic-level stories written in it (along with some other things that aren't as relevant). So all races know Common and usually their regional language, but their level of expertise in either of these does vary on how much they've been educated.
"Islic" / Common
The language of the Isle of Shattered Stars is equivalent to Common compared to other Universes, and is the basic "common knowledge" language that all races naturally gain over time as they age to adulthood. Despite it being learnt through Magninium exposure naturally, it is called Islic as it is the only language the Isle supports and will do trade or diplomacy in. As the Isle plays a massive part in international politics, it is considered the formal language and is used for all legal documentation.
Cadavan Runic is the name given to ancient writings in Cadava, based partially on the cracks formed in the ice by Worldshear's liquid seeping into the continent. It is primarily a written language, with almost no speakers, and is typically used for high-level enchantments and runes due to its ability to process magic. It is incredibly difficult to learn, and most enchanters prefer using Common simply for ease of use.
Lacraeic / Old Verebrivan
Lacraeic is a distinct dialect of Common that grew out of the isolated continent. It is similar enough to Common that speakers of the two can understand one another, but does differ somewhat in phrasing structure and pronunciation. Lacraeic was originally taught to members of the Verebrivan military as part of a compulsive education, and was spread to the rest of Lacraya through its occupation of the continent. It is considered the 'proper' language of Flames by the Holy Empire.
Purren is the language taught in Maweth schooling, as dictated by Mewt Mavet himself. It is a descendant of the Chendren language, though based on the original church's formal dialect with many new Common loanwords. Purren is the national language and all government affairs are to be handled in it. Only international diplomats and ambassadors' documentation, treaties, and trade deals may be made in Common - though a Purren copy must also be provided. Purren is so ubiquitous in Maweth that many speakers are somewhat unfamiliar with Common.
Chendren was the primary language spoken in the country of Chendre, a small theocratic nation on Chellabra. During Mewt Mavet's rise to power, Chendre and the other states of Chellabra were absorbed into the mega-country Maweth, and their languages stamped out - including Chendren. Despite this, the cult of worship surrounding Mewt, the Dewclaws, use Chendren in code and to speak privately with one another. Its use among the cult is not hidden, though Mewt mindwipes anyone's understanding of it if they choose to leave the Dewclaws in order to preserve its secrecy.
As Chendre was highly dedicated to the Ardor, especially Mesechev, many surviving religious texts depicting the Ardor in godly forms is in Chendren. Translators still exist for it, though many of those books have... mysteriously... gone missing recently.
Passen is used across Bivve, both by its instigator Passane and its enemies. It is a short and simple language, using the inherent intent in Magninium to convey larger ideas while speaking swiftly, deliberately, and clearly. Best used for conveying messages across large distances, it is perfect for the highly militaristic Passane. Eager to learn Passane's military movements and propaganda, it became common to learn in other Bivve countries, and has somewhat unofficially become its third universal language, after Common and Averillen.
Averillen was the original language of Alleria, the province that would birth warlord Unea. Unea went on to conquer the entire center valley of Bivve, forming the Kingdom of Alleria, which became the Federated Union of Alleria when she died and her daughter sought to give the member-states power back. Despite the shift in power back to the states, Averillen remained the language in use within the Union, especially as Passane conquered more territory and enforced its own language. Small pockets of original Allerian languages persist in some regions, but are largely dying out.
The other free states on Bivve - Tashen and the city-states of the Western Dominion all use Averillen as their official languages as well.
Varish is an obscure and difficult language spoken only in the Vaervan Kingdom. Averillen is a common second language, with Islic making up the third and Passen the fourth. Though there are speakers of Varish outside the Kingdom, they are few and far between - and are not typically interested in serving as tutors or translators in part due to the difficulty of speech. All denizens of the Vaervan Kingdom are expected to speak Varish, including the rare immigrants - learning it "on-the-fly" is deeply frowned upon.
The written alphabet appears similar to Braille, and is raised.
A language often described as "snappy" and "aggressive" by foreigners, the Serene Tongue hails from Sarens and bears some similarities to Holysong, the language of neighboring Iah-Yah. Some linguists believe it to be a dialect of Holysong that eventually evolved its own lexicon from separation and slang, though the people of Sarens vehemently deny this, and claim their language was gifted to them by the sun and moonshards. Unlike Holysong, the Serene Tongue has a written alphabet that resembles Islic's in many glyphs. It is considered somewhat uncouth for foreigners to speak the language if they do not intend to immigrate to Sarens, as doing so "defiles" it.
Spoken by the elite castes of Iah-Yah, Holysong lives up to its name; non-speakers note it as melodic and high-pitched, with some assuming Holysong speakers are genuinely singing when they speak. The language depends heavily on inflection to communicate ideas and conjugation, hence the intense shifting of tone. It is considered an educated language, hence the adoption by higher castes and usage in government within Iah-Yah. Lower castes alternate between Islic/Common, some Holysong, and bits of the Serene Tongue.
Holysong has no written equivalent; Iah-Yah uses Common/Islic as their written language.