@diba: I *think* that this is not directly related to the localization, but to the keyboard layouts that come bundled with the Kindle.
For some reason, KT keyboard layouts have never been prominently addressed in this thread. I guess all the russian folks figured it out among themselves
. I do recall some requests for a czech keyboard, and for a chinese one.
For all but the russian (which can be found on relevant pages), and the chinese (which is probably impossible with the current Kindle) ,they seem to never have been gone any further... probably because the KT keyboard is "good enough" for most of us reading here -- it includes the latin characters, and also many "extended" latin characters, out of the box.
I took a look at the keyboard specification files (which are pure XML, by the way). They are all pretty simple to understand, and it is (IMO) very straightforward to write keyboard layouts for the KT.
So finally coming back to your particular question: At this moment, I do *not* recommend using the german keyboard. The simple reason is that all german letters can be easily obtained from the "english" keyboard. (For instance: long-press "s", and you get the "ß" option).
More importantly, the german keyboard (and I suppose many others as well) are *NOT* complete. There is a separate "numbers-only" keyboard layout, which is required for the locking and unlocking of the device ("Settings -> Security Code" or similar). If you don't use the default keyboard, you may be screwed.
PS: in this post, I'm only talking about the keyboard layouts which are initially distributed with the KT. I do not know if there are, nor am I addressing, "keyboard packs" for individual languages.