To decide on the religion’s official language, we should choose which species the prophet(s) belonged to. The other option would be the god’s language, should one exist. It could also be the language of those the god most wishes to reach, which could be a species other than the prophet’s. For older religions, the language could be one no longer spoken, such as Latin, which can make it unique, prized, and mysterious. Holy texts are likely written in the official language unless translated.
Choosing where this prophet became one can help determine a likely species, but arguably most religions will want to convert other species, too. If they’re not considered worthy, by mortals or a god, this inclusion or exclusion will determine the availability of translations to other languages. Even if the clergy don’t create them, others may. The willingness to reach others will also decide which, if any, species languages clergy are expected to know and to what degree.
Place in Society
It can be difficult to generalize a religion’s place in society because this will depend on the society. It might be a state religion in one place and banned in another. What we want to decide is, for places where it is accepted, what role can it play in society and the lives of individuals?
For example, it could be prominent at sporting events if the religion promotes athletics or prowess in battle. Priests could be blessing the games or acting as fair judges. If the religion helps alcoholics and others similarly afflicted, it can provide hostels or treatment for free, perhaps with backing from the settlement or sovereign power (which is paying their bills). Which religion’s priests perform marriages, burial rituals, or life’s milestone ceremonies? All of this will be based on the god(s) we’ve created and what they care about.
One reason these matter is that members of a society will think of a religion’s reputation when it is mentioned, their buildings are passed, or their priests are encountered. Even the followers, if wearing the religion’s symbols, can elicit a reaction, whether subtle (a frown or smile) or excessive (taunting). Arguably, every character we invent should have a religion (and might have switched in their past) or none, but there’s typically a reason for the latter, such as trauma or upbringing causing loss of faith. This will, in turn, cause their reaction to their own or other religions and such details are realistic.
Invent religious customs based on a deity. A god of war might want a show of strength that results in a firm handshake. The words might be bold and decisive, such as, “Fierce is the heart!” A god of peace might wish blessings and be gentler in touch. A goddess of pain might slap a hand painfully. We can invent these beforehand or while writing. They often don’t need explanation because the depiction tells the audience what they need to know. Refer to chapter 1 on creating cultures for what to invent, using the deity as inspiration.
Some religions may send clergy out as missionaries early in their career; older priests are more established in the community and will be missed if sent far away. They can be inspired to do this or commanded to by clergy or deity. Are they aggressive or passive about proselyting? The same religion might be aggressive in one area and less so elsewhere due to local leadership or situations among those to be “saved” by conversion. Determine if there’s a set number of years this work must be done.