Three things can be said about the expression my brethren:
(1) This expression is used fourteen times in the letter and often signifies a transition to a new subject matter (for example, 1.16, 19; 2.1, 5, 14; 3.1; 4.11; 5.7, 12, 19).
(2) This affectionate address sets a pastoral tone for various exhortations of the letter. The Jewish people in the Old Testament used the word brethren to describe not only members of their own family but also their fellow Israelites. In New Testament times it is often used to refer to fellow Christians in the community. They are fellow members of the family that acknowledges God as the Father. Clearly, when James addresses his readers as my brethren, his feeling toward them is that of warmth and love.
(3) The use of the plural form brethren is general; it does not mean to exclude “sisters” who are also of the Christian community. It is therefore possible, indeed desirable, to render it as “my brothers and sisters,” as the New Revised Standard Version (New Revised Standard Version) has done.

In certain languages a literal translation of the term brethren will refer to actual siblings. In this case translators will need to avoid such terms and simply render it as “my friends,” as in the case of Revised English Bible and Good News Translation; or we may say “my fellow believers [or, Christians],” or even idiomatically “my elders and youngers.”

The word joy in Count it all joy is related in meaning to the word rendered “Greeting” in verse 1. The similarity in sound between the two words in Greek seems to suggest that a play on words is intended. The meaning of Count is “to reckon as,” “to deem as,” or “to regard as.” Most modern translations render it as “consider” (so Good News Translation, New International Version [New International Version], New Jerusalem Bible [New Jerusalem Bible], New Revised Standard Version). The force of the word all modifying joy is sometimes understood in terms of completeness, meaning that the joy should be pure and unmixed; for example, “nothing but joy” (Barclay’s translation [Barclay], New Revised Standard Version), “pure joy” (Moffat [Moffatt], New International Version). Others take it to mean the intensity and quality of joy; for example, “greatest joy” (Goodspeed’s American Translation [Goodspeed]), “great joy” (New Jerusalem Bible), “supremely happy” (New English Bible/Revised English Bible).

A literal translation of the clause Count it all joy presents difficulties for translators in many languages. In such languages a more natural translation will be “You should rejoice greatly when…,” or more idiomatically “Your hearts [or, stomachs] should feel very warm when…,” “Your hearts should dance when…,” or “Your innermost being should ring when….” In languages where it will be unnatural to talk about being “joyful” when encountering trials, it will be helpful to translate in a similar way to Good News Translation, “consider yourselves fortunate,” and say “You must understand that it is beneficial for you when…,” “… it is a great advantage for you when…,” or even “You must feel great satisfaction when….”

It is significant that the readers are commanded to have a sense of happiness and joy, or even “satisfaction,” in the face of trials. Trials are something that Christians meet or “face” (New English Bible, New International Version, New Revised Standard Version), things that “come your way” (Good News Translation) or “come upon you” (so the King James Version [King James Version]), referring basically to inward impulses and experiences that may entice a person to sin. This is obviously the sense intended in verse 13. The word, however, also means “testing,” referring to outward troubles and difficulties. The corresponding verb is used of a young bird “testing” its wings, of “testing” drugs to see if they could cure diseases, of God “testing” Abraham to offer his son as sacrifice (Gen 22.1), of the Queen of Sheba “testing” the wisdom of Solomon (1 Kgs 10.1), and so on. In biblical usage the “testing” often leads to a good end. It is to cause the person being tested to emerge stronger and better, in loyalty and in faith. Most probably the second meaning, namely outward troubles, is the intended sense in the present context. While not ruling out the possibility of sufferings and persecution, the context appears to indicate that the word trials here probably means nothing more than daily troubles of some sort. So this final sentence may also be expressed as “When you pass through [or, endure] all kinds of troubles [or, difficulties].”

Quoted with permission from Loh, I-Jin and Hatton, Howard A. A Handbook on The Letter from James. (UBS Handbook Series). New York: UBS, 1997. For this and other handbooks for translators see here .