Modern English belongs to the West Germanic branch of the Indo-European family, and for most of its history it was a receiving language for religious material rather than a composing one. The texts that shaped English religious life arrived in translation: the Latin Vulgate, then Wycliffe, Tyndale and the King James Version out of Hebrew and Greek; the Buddhist and Hindu canons out of Pali and Sanskrit in the nineteenth century; the Islamic sources out of Arabic. English readers met almost everything at one remove.
That changed in the nineteenth and twentieth centuries, when English became a language in which whole religious and esoteric systems were first written down rather than a language they were carried into. The Hermetic Order of the Golden Dawn drafted its rituals and its tables of correspondence in English. Theosophy, founded by a Russian-speaking writer, published its major works in English. Thelema, Wicca and the wider modern Pagan revival composed their liturgies in English from the start, as did a long line of new religious movements from the Latter-day Saint tradition onwards.
The distinction matters whenever a claim is made about what language something was written in. A text composed in English and a text merely available in English are different objects, and the difference decides where its vocabulary came from, who could read it first, and what a translator has already done to it on the reader's behalf. This atlas keeps the two claims apart and treats the language a text was composed in as a fact about the text, not about its audience.