Common

Almost all sentient beings can speak this language, and it is the de facto tongue of any interracial communication. Though largely spoken as a second language, it is by far the most prevalent language in Quirus, though few can read or write in Common.
Though an immense number of local dialects exist, the language is spoken remarkably similarly by even the most distant of populations, owing to its capacity and prevalence as a trade language. Though it has been the language of Humans since time immemorial, it came to global usage in the the third and fourth eras, with the population explosion of the Human race and its dominance in maritime trade activities. 
While any native speaker can convey complicated thoughts and emotions via Common tongue, few secondary speakers use it in any capacity outside of trade, thus limiting its usefulness in most non-Human societies.