I'm running Klettres on Debian Wheezy Stable. The Arabic alphabet is apparently not available. Nothing happens when I try to download if from within the application.

Is there somewhere online where I can find the necessary file(s) to install it manually? I e-mailed the author and received no response.

Which version of KLettres are you trying to use?
Also, try starting KLettres in a terminal and watching the output when attempting to perform a download to see if that indicates what the issue might be.