I added a Russian keyboard to 5.3.2 quickly and easily, so I thought I'd share. My apologies if this is already known; I poked around and didn't see the same info.
It looks like the standard method is to overwrite the Italian keyboard, but this is not necessary.
1) I found a Russian keyboard layout "it-600x800.keymap" and "it-800x600.keymap" somewhere in here:
http://www.the-ebook.org/forum/viewtopic.php?t=22586. I can't read Russian, but google can. Sort of. I think the credit goes to eureka? Sorry if I'm off on that one.
2) Copy the contents of /usr/share/keyboard somewhere, and make a directory "ru" inside it. Put the keymaps above inside, gzip them, and change the "it" in the filename to "ru".
3) Copy utils.so from keyboard/it/ into your Russian directory "ru". Open the file in the editor of your choice that won't wreck binary files. Change the string "kb-it" to "kb-ru", and the string "Italian" to "Russian". (Note that strlen("Italian") == strlen("Russian")).
4) rebuild keyboard.cramfs.img and copy it over the existing one in /usr/share.
5) I had to reboot - no idea how many services have to be restarted to let umount do it's thing.
Now I have a Russian keyboard, and still have an Italian keyboard. It even showed up in the keyboard picker without any more fiddling.
OK--- I sure hope that's what I did. Most of my hacking is done in rushed 5 minute increments or it doesn't happen at all :-(.
Cheers!