If he does not listen is the negative of the phrase in verse 15. “If he does not admit he has done wrong” or “If he does not pay attention to what you say” are ways to translate it.
To say next take one or two others along with you implies a second visit to the person. For some languages this will need to be made explicit, as in “go see him again, but take one or two other people with you.”
One or two others (so most translations) is literally “one or two.” Good News Translation has “one or two other persons,” and the full meaning will be “one or two other Christian brothers.” This is the second step in winning back a lost brother, and it has its basis in Deuteronomy 19.15: “Every accusation may be upheld by the testimony of two or more witnesses.”
Word (Good News Translation “accusation”) may refer here to either (1) the charge brought against the brother (Jerusalem Bible “the evidence of two or three witness is required to sustain any charge,” and Good News Translation “every accusation may be upheld by the testimony of two or more witnesses”) or (2) the discussion which results between the brother who has sinned and the one who discusses the matter with him (Phillips “so that everything that is said may have the support of two or three witnesses”). The latter interpretation is probably correct, as one commentator remarks: “The presence of one or two of the brethren is meant to protect the sinner; the admonisher may well be wrong, or someone else may find the right words when he cannot.” Translators who follow this interpretation will say something like “so that the things you point out to him can be confirmed by two or three other witnesses (or, people)” or “so that two or three others can confirm the things you accuse him of.”
“As the scripture says,” though not in the Greek text, is included by Good News Translation to indicate the nature of the quotation. This is especially important for hearers of the Scripture, for whom the quotation marks (or the inclusion of the words in italics, as with New Jerusalem Bible) will mean nothing. There are actually several ways to indicate this is a citation, should translators wish to do so: “Do this in order to follow the Scripture that says that two or three witnesses are needed to make an accusation against someone” or “The Scriptures say that you need to do this before you can accuse someone of doing wrong.”
Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .