that you have not only read "The Hobbit" and " The Lord of the Rings" in your own language

I'm not sure if I understand this correctly. Does "in your own language" mean that the children have read German translations (the letter is addressed to a school in Germany) of The Hobbit and LotR? The first German translation of LotR was published in 1969/70 but this letter dates back to 1964. That's five years before the German translation was published.
But maybe I don't get the point