The language frequently described as “Common” is a piecemeal collection of phrases and terms from the many different languages used in the various nations. It sees frequent use among traders, travelers and adventurers, but practically never sees use in any official or formal interactions. It may help to think of the name to be “Common” in the sense of “Shared” and not “Common” as in “Frequent.”
Since it's assembled piecemeal from other languages Common doesn't have a proper written equivalent. Most legal documents (contracts, political decrees, records, etc.) are still written in the prevailing language in the region.
While in most places Common doesn’t see much use beyond the “street level,” one notable exception to that rule is in the Crossroads. Since so many of the people moving through the area or selling in the market place are from different areas it’s essentially become the standard language in the city.
In general terms each of the five human nations has their own language. While there is a small amount of cross-pollination speakers of one tongue will be unable to communicate with speakers of another.
Lilting and partial to vowel tones, it’s commonly said that the language of the Thells is a language in three parts with verbal, written and gestural components. In general the language is fairly direct but allows speakers to become verbose and flowery should they wish to with great ease.
The Arad tongue is difficult for those who aren’t native speakers to pick up more than a smattering of (especially for speakers of more direct tongues like Thell or Plain Speech). Non-native speakers tend to poke fun at Arad’s excessive word lengths for seemingly simple concepts and tenuous relationship between the written language (which relies on an implied presence of vowel sounds rather than representing them with actual characters much of the time) and the spoken language.
Anyone who has spent more than a few days with an Arad speaker will have likely picked up a few key terms such as “Drink,” “Battle,” and “Riches.”
The language of the people of the Principality of Helladhil tends to consist of many short abrupt words and phrases. The written language uses a system of pictograms for abstract concepts rather than specific phonetic character representations making it a difficult concept for speakers of many other languages to grasp.
Curt and to the point the language of the Plainsmen doesn’t tend towards waste or eloquence. As a side-effect of the direct nature of their native tongue many Plainsmen who learn other languages are usually considered to border on rude or bossy when using them with native speakers.
The language of the people of the Southern Reaches.
As a race with a long history the Elves (as a whole and as their various sub-races) have seen their languages evolve and change over time. In general practice as it stands at present there are three different Elven languages.
While the Elves of Adrindest and Egiolin still maintain communication they have seen an increasing separation between their localized versions of their shared ancestral tongue. In general it is still possible to communicate for speakers of the different tongues, though there may be some terminology or phrasing that may be problematic and can lead to some uncomfortable miscommunications.
Abandoned except by historical scholars or sages Old Elven is essentially a dead language. There are still many ruins and ancient artifacts carved with Old Elven words, most of which are meaningless to speakers of the modern Elven languages.
As part of a single nation the Dwarves have worked to keep their language from undergoing too much fragmentation. A few different regional and sub-race accents may be encountered, but by and large the Dwarven language itself is a single consistent tongue.
Another fragmented language (much like Elven), in this case caused by the geographic separation of the Rock Gnomes (residents of the Realm of Mithlome) and the Forest Gnomes (residents of the Republic of Adrindest). Because of the divergence between these two languages they cannot be used for cross-language communication.
While it doesn’t share more than a handful of linguistic borrowed terms with Wood Elven, Forest Gnome is usually spoken with a similar accent and cadence to Wood Elven.
From their time among the Dwarves in the Realm of Mithlome the Rock Gnome language has picked up a fair number of shared words from Dwarven (especially with regard to technical terms and information around trade skills).
The Halflings consider their language something of a hallmark of their racial pride. Regional accents are subtle and the language is very consistent across almost all speakers. Halflings rarely teach their tongue to non-Halflings largely because it bothers them when “tall folk” fail to grasp the more nuanced aspects of the language.
Guttural and harsh, the language of the Orcs is usually only spoken in whispers before an ambush or other battle. Few non-Orcs know the tongue in detail, but it’s not uncommon to meet an adventurer who knows a few choice off-color phrases or offensive terms in Orcish (often picked up from an opponent in combat).