Usually, but not always, based on the tongue of a capital city, a standard language is defined by the selection of certain regional markers, and the rejection of others. This is the version of a language that is typically taught to learners of the language as a foreign language, and most texts written in that language follow its spelling and grammar norms.
Some of the features that identify a standard language include:
In Norwegian, for example, two parallel standard languages exist, one called Bokmål, based partly on the local pronunciation of Danish back when Norway was ruled by Denmark; and a second, called Nynorsk, based on a mixture of dialects from western Norway. While Italian contains dialects that vary from each other even more than the two versions of Norwegian do, there remains a single standard Italian; curiously, standard Italian is not based on the speech of the capital, Rome, but on the speech of Florence. Standard Iberiann Spanish is likewise not based on the speech of Madrid, but on the historically more northerly province of Castile.
Other standard languages present fewer complicating factors. The pre-eminence of Parisian French has reigned largely unchallenged throughout the history of recent French literature. In British English, the standard Received Pronunciation is based on the language of the upper classes in the London area, and is based on the dialect that comes out of the British private boarding schools. In the United States, since Washington, DC is a planned city devoted almost entirely to government, with no claim to historical pre-eminence, the standard of American English is based on the speech of the upper Midwest. English has no official legal status in the United States as a whole; curiously, the languages that do have official recognition are Spanish and Hawaiian; Spanish is guaranteed equal treatment for legal purposes in the territories acquired by the United States from Mexico by the Treaty of Guadalupe Hidalgo, and Hawaiian enjoys similar status in Hawaii
See also, and compare: Official language