In December 1841 at age 60, Frances wrote,
"I have this summer mastered Syriac enough to know that with a previous knowledge of Hebrew and the Chaldee verb differences, you have only the characters to learn, an ugly bungling device, from which, however, the Cufic* is mainly borrowed, and to which the modern Arabic has some little obligation."
Here is a woman who not only had the discipline to learn ancient languages, she also understood their development.
Her letter continued: "Arabic I am now rather hot upon, have exhausted the little vocabulary I have here, and am most anxious for a lexicon; do you know of a Castell? but I believe a modern German one would do better, except that Latin suits me better than German."
So, she needs a better dictionary to help her translate Arabic. An Arabic-German dictionary will do, but an Arabic-Latin one would be better.
By this time she already has Hebrew, French, German and some Danish—at least.
*Cufic or Kufic is an early angular form of Arabic script found mainly in decorative inscriptions.