"Colonial English" is the term used for the primary language spoken in the Republican Star Cluster. It was invented with the colonization of the star cluster by an informal mixing of languages from the various people who settled.
While it's base may be that of the language spoken on Earth, Colonial English is a bastardization with common words and phrases adopted from mostly from Chinese and Spanish. Each world has its own variation, depending upon the people's that settled there while other worlds, such as worlds of the Hwon System speak "Colonial Spanish". On Galileo the mix of languages skews toward Chinese and Russian. On Athena it is filled with Turkish words and phrases. On New Normandy, it is a heavy mix of Spanish and Eastern European languages.
The Republican Fleet operates a language school on Troy as part of its basic training that attempts to normalize, as much as possible, the various dialects to provide smooth communication in the military.
There is no one world that speaks "standard" Colonial English. Rather, each has its own flavor (or none at all). Despite the differences across the worlds, standard Earth English reamins the primary written language while standard Spanish and Chinese are close seconds. The Unified Republic of Stars publishes all official documents in all three languages as well as Arabic and Hebrew for dissemination to the people of Al Gharbiyah and Madaba which do not speak or read any version of English.
Colonial English is often unintelligible to people from Earth because of the various inflections put on words and syllables that were influenced by the various accents of the people that settled the worlds. Additionally, they are left in the dark culturally because of new common metaphors and references introduced into the language that may not even have originated in English at all. This has been a problem during periods where the UUHA has occupied Republican worlds and they often find themselves having to recruit or demand the help of locals when communicating to the people, such as in the famous case of Ayla Athena in 2174 durring the Second Republican Defensive.