Verse 19 looks back at the previous argument, including 8.4-5, while verse 20 introduces a new thought. Both the contrast with verse 19 and Paul’s change of direction are well produced by Good News Bible‘s “No! What I am saying is….”
What pagans sacrifice is literally “what they sacrifice.” It will be helpful for a translator to expand this clause as Good News Bible has done, in order to show where the sacrificing occurred: “what pagans sacrifice on altars.”
The verb that is translated sacrifice is the same as that translated offer; Revised Standard Version and Good News Bible have variety for reason of style. This verb often applies to the killing of animals for sacrifice, and is therefore narrower in meaning than the English “to sacrifice.”
The square brackets in the UBS Greek text around the word translated offer indicate that there is some doubt about its position in the text, but there is no question that it belongs there at some point.
Revised English Bible and New Jerusalem Bible make explicit the fact that Paul is here using the language of Deut 32.17. However, he employs a present tense, they offer, rather than the past tense, “they offered.” Other than that, the quotation is the same. New Jerusalem Bible shows this point by italicizing the quoted words, while Revised English Bible marks the quotation more emphatically by translating “pagan sacrifices are offered (in the words of scripture) to demons and to that which is not God.”
The word demons could refer to good spirits in secular Greek, but almost never in the New Testament (Acts 17.18 is an exception). Phillips‘ rendering, “evil spiritual powers,” is therefore correct and accurate. Certain languages refer to these as “evil spirits,” or even “filthy (or, dirty) spirits.”
The and in and not to God is natural in Greek, but not good English style. Good News Bible leaves it out. Many other languages can do the same.
Quoted with permission from Ellingworth, Paul and Hatton, Howard A. A Handbook on Paul’s First Letter to the Corinthians, 2nd edition. (UBS Handbook Series). New York: UBS, 1985/1994. For this and other handbooks for translators see here .