Galactic Basic Standard

Galactic Basic Standard (or Galactic Basic or Galactic Standard or Galaxy Standard) was the most prevalent and most used language in the Galaxy. Based off of a mix of early human languages, Durese, and Bothese, Basic started as a slang or jargon of traders, and spacers. Because of its popularity with members of those professions its popularity and acceptance spread. It was the evolution over the earlier Old Galactic Standard. In this evolution, Old Galactic Standard was influenced by Dromnyr, the language from planet Vulta. Under the Galactic Empire, a version of the language was known as Imperial Basic.

Most sentient species that made galactic contact could and did speak Basic in addition to whatever native or regional language they might have used on a daily basis. Some beings did not possess the organs necessary to speak Basic, including Polis Massans, Ssi-Ruuk, P'w'ecks, Wookiees (with the exception of some Wookiees whose vocal cords were different from baseline Wookiees), and a number of insectoid races. Most Gamorreans could not speak Basic, though there were exceptions (such as Governor Kugg.) Whether or not a being could speak Basic, it was usually in their best interest to comprehend it, and most did.

The Towanis taught the Ewoks a mysterious and undocumended language, which didn't help them understand Leia, and later, Han Solo and Luke who spoke Basic. The relation of that language with Basic is not known.

Basic used the Aurebesh script.

Behind the scenes
In both the films and books, Basic is the same as English. In translations to non-English languages, Basic is assumed to be reciprocally the same language as the one being used. As a result, spoken Basic is considered dubbed and Aurebesh text is considered translated. As in the Lord of the Rings books, the "dubbing" and "translation" had some implications. For example, dialects in English belong to different in-universe accents in the movies. Ewan McGregor's and Ian McDiarmid's accents are for example Coruscanti accents in the movies. Imperial characters had English accents while Rebels usually had North American accents. Other accents are also heard, such as Jamaican (Gungan Basic), Irish (Emon Azzameen), Asian (Neimodian) or Russian (Juhani).

In E.T.: The Book of the Green Planet, which possibly shares its continuity with the Star Wars saga, a character mentions that she needs help with her "basic."

Original etymology
Star Wars authors have coined original English-like words derived from real English elements but which don't exist in English language; they seem useful to a space-driven civilisation of the Star Wars characters, but totally useless for our daily language. Such words are 'speciesism' (equivalent to racism, but against sentient beings other than us), 'gentlebeing' (gentleman other than a human), 'offworlder', 'bird' (slang for spaceship, cf. how US Navy slang calls 'torpedo' as 'fish'), 'hyperspace', 'spacer', 'Sentientologist', 'youngling' (young + suffix -ling meaning 'person') and other technology terms like blaster, droid (from android), durasteel etc. See slang.

However Basic vocabulary includes some totally original, of inexplainable etymology and origin, words also unrelated to English, like Moff, Jedi, Padawan, Darth etc or even compounds like Sithisis. It is possible that such words are derived from alien languages.