Translation
However, in the assembly of the called-out ones, if there is no interpreter, he
Go to footnote numbermust keep silent; and he must speak to himself and to God.
Paraphrase
But when the church is gathered for worship or prayer, if no interpretation is given by God, the one or ones who claim to be speaking in the proper form of public tongues should stop because, in your case, the interpretation is needed to confirm that the speaking in tongues is authentic and not a counterfeit. Instead, the person who wants to speak in tongues should choose the private type of tongues in which he communicates with God through groans, sighs and tears and no one hears it except God.
Footnotes
1
The antecedent of “he” in this verse is “if anyone speaks in an unknown tongue” from the previous verse.
WHY WAS AN INTERPETER ALWAYS NEEDED IN CORINTH?
An interpreter was needed in the meetings of the church in Corinth in order to allow the local believers to confirm the message if there was the claim that their speaking in tongues was for the benefit of the foreigners present. Here Paul was anticipating them saying that an interpreter is not always needed, which is true in other settings where everything is being done properly, but in Corinth, it was important to avoid further abuses. Paul would not require an interpreter in other situations, unless similar abuses were present. I believe Paul had been informed by God that the Holy Spirit would provide the interpretation if true public tongues were given by the Holy Spirit in Corinth in order for everyone to know it was the real deal.