When you give alms translates the same structure used in verse 2.

Do not let your left hand know what your right hand is doing: Die Bibel im heutigen Deutsch is similar to Good News Translation: “so that your best friend will not know about it.” A number of commentators believe that Jesus is speaking of a generosity that even one’s most intimate friend must not know about, and at least one commentator notes that the interpretation as a reference to one’s closest friend finds support in a current Arabic proverb. But whether the reference is to one’s best friend or to one’s self, the focus is on the secrecy of the action. Jesus is here calling upon his followers to disregard self in the giving of gifts for the needy. Giving is to be for the sake of the poor and not for personal satisfaction. In giving, one is not to seek praise from God or from people; a person who truly loves God and others does not think of self.

Many translators have felt that their readers will have no trouble understanding a literal translation of this verse. The idea of the secrecy of the action is clear. Others have felt that the idiom needs clarification. Some have followed the model of Good News Translation, where the reference is to one’s best friend, but many prefer to be more general, as in “do it so that no one else will know about it.” The sentence may be “When you give to help some needy person, do it in such a way that no one will know what you have done” or “When you give to people who don’t have all they need to live, give help to them in secret.”

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 .