1. GRADUALLY MODERNIZE THE TEXT ITSELF. On a periodic schedule, perhaps, change the language incrementally to a form that has increased intelligibility. This is logically possible, although no religion seems to do this deliberately (although it surely takes place automatically and unavoidably in an orally transmitted literature). Why is incremental text modification decried by religious authorities? Probably because of the appeal of sticking with the traditional, ``official'' text as long as possible. Still, in 20 century US, new English translations of the Bible are written on a regular basis these days. Maybe the Bible will never slip out of date again!
2. PERMIT NO CHANGE. Allow no revisions of the text. Instead either (A) train a group of professionals (eg, monks or priests) who continue to read and understand the now-ancient language and interpret it for modern laypersons, or (B) train most or all followers of the religion to read the ancient language competently.
The Catholic church followed Plan A from about 400 CE until about 1900CE. Monks and priests read and interpreted the Latin text for believers. Islam and Judaism have largely followed Plan B, where believers typically learn either Classical Arabic or Ancient Hebrew (The Bar-Mitzvah ceremony is, in part, a public demonstration of competence in Hebrew for young male Jews). Hinduism and Buddhism also followed Plan A where a priesthood of Brahmins (for the Hindus) and monks (for the Buddhists) read and interpret the sacred scriptures for untrained lay people.
3. TRANSLATE SACRED TEXTS INTO THE CURRENT IDIOM -- from a source language (the language of the original text) to a target language (the language being translated to) of the community of believers. But this immediately raises several further questions.
A. Which version of the ancient text should be relied on? For example, there are literally hundreds versions of the Greek bible that survived the ages. There are also many versions of the Hebrew bible that survived until about 800 CE when a Jewish canon was agreed on. These differ in many respects - in inserted `clarifications,' accidental errors and some deliberate revisions to support specific theological positions. Disagreements arise, of course, as to which version is really the `right' one or the `best' one. But this is the easy problem.
B. How `literal' should the translation be? Since the sacred texts are taken to be the actual words of God or to be divinely inspired, ``free translation'' (or `dynamic translation' as it is sometimes known today) are often received as heretical reinterpretations of sacred text.
1. Because a single word in one language often has meanings that require several words in another language For example, the Greek word angelos could mean either `divine messengers' or `Jesus' disciples'. The English word `wall' could be translated into German as Wand (inside wall, partition) or as Mauer (exterior wall). Word for word translation is out of the question.
2. Because grammatical particles (like articles, verb tenses, case markers, singular/dual/plural, etc) do not exist in every language leading to multiple ambiguities (from the perspective of a target language like English). For example, a Russian sentence literally translated as `Boy threw ball.' needs two articles in an English translation, either a or the for boy and for ball. Only the context of the sentence could tell us which to use for the English translation. Not using ANY articles at all produces nearly unintelligible English. The Japanese sentence rendered literally as `Remove front wheel' could mean either `Remove a front wheel' or `Remove both front wheels'. Which is the correct translation depends on the context.
3. Because idioms that have obvious meaning in one language and culture may be completely confusing to speakers from another language and culture.
For example, the Hebrew phrase translated literally as `the stalled ox' or `the ox that was in the stall' is normally translated in English bibles non-literally as `the fatted calf' (in the King James Bible, or as `fattened calf' in modern English translations). This free translation is appropriate since keeping an animal in a stall and overfeeding it is how a herder fattens an animal for slaughter, and since Hebrew used the same word for adult and immature cattle but only calves were fattened in their culture. This idiom was as obvious to the ancient Hebrews as it is to us that `keep your eyes peeled' means `stay alert' (not `do not allow your eyes to blink') and `stay on top of it' means `pay attention to it' (not `sit physically on it'). But `the stalled ox' is not readily interpretable in English, so even the King James translators (who generally tried to be literal) employed something more idiomatic in English. The bible contains thousands of similar examples.
English Bibles can be located along a scale from `most literal' to `least literal' (or most given to paraphrase). The Zondervan Bible company suggests such a scale.