- https://en.wikipedia.org/wiki/Kaddish#History_and_background :
Professor Yoel Elitzur … argues that the Kaddish was originally written in Hebrew, and later translated to Aramaic to be better understood by the masses. He notes that quotations from the Kaddish in the Talmud and Sifrei are in Hebrew, and that even today some of the words are Hebrew rather than Aramaic.
That’s quite an interesting and surprising point of view. And quite comprehensible and logical as well.