Galactic Basic is the common language of the galaxy, used for communication between many different species. Although the exact origin of the language is lost to time, it has been proposed that it was constructed from a mixture of the native languages of the founding members of the Old Republic, including the Duros, the Zabrak and Humans.
Most sentients are familiar enough to other languages to understand them, even if they prefer to speak a language specific to their species or region. Many interspecies conversations are multilingual.