Translation vs. Transliteration: Mystery

Kenny has another post in his translation vs. transliteration series, which I believe started here, where he mentions angel, apostle, Christ, evangelist, hades, gehenna, etc. I have been thinking about a few others, like bishop, deacon, eglise (church in French) and synagogue. There are many more.

In this more recent post Kenny tackles the word 'mystery'. After discussing relevant background material he concludes,

The mystery was not revealed in former times, but it has now been revealed by the Spirit, and Jesus gave us special instructions as to what to do with His secrets: "Whatever I tell you in the dark, speak in the light; and what you hear in the ear, preach on the housetops" (Matthew 10:27, cf. Luke 12:3).

I conclude, therefore, that the New Testament's use of this word implicitly sets up a contrast between Christianity and the Pagan mystery cults: whereas the Pagans carefully guard their mysteries, the Christians are eager to announce them from the housetops! God's revelation, once given, is given to all mankind. All are welcome and invited to come and learn the mysteries of God. You need not go to any particular location or perform any particular ritual: we, the Church, will come to you to teach you the mysteries God has revealed to us.

This creates something of a difficulty for the translator, because modern audiences do not have familiarity with these kinds of religious "mysteries." As I mentioned, we have some secret societies that resemble the mystery cults, but modern religions tend not to work this way (although Mormonism does have some rituals that are open only to higher-level members of the church). As such, we do not have a term for this.

The Eastern Orthodox Church continues to use the word "mystery" to refer to a mystical ritual, but this isn't quite right for Paul's usage either. Mystery is the word used in references to these things in writing about Greek culture and religion, so if the target audience of a translation is made up of hellenists, then keeping the word mystery is appropriate. Also, many "church people" have been taught the Pauline meaning of mystery as something that had never before been revealed to mankind, so this audience, although it doesn't catch the implicit contrast with Paganism, does get the correct meaning. But what about translations for more "mainstream" audiences?