Q. Why is the Kaddish in Aramaic and not Hebrew?
A. For a long period Aramaic was the Jewish vernacular, though the more learned people were adept at Hebrew. So as not to exclude the unlearned, the Kaddish was formulated in Aramaic. In recent times, when hardly anyone speaks Aramaic, there were attempts to introduce the use of a Hebrew version, but public feeling preferred the text they were used to.