When surf around official site of the Duokan, I found this
~ ChangeLocale en-US.utf8
And it give me an idea that maybe this could be a way to change language quickly to Turkish with a command like
~ ChangeLocale tr-TR.utf8
Ofcourse it didnt work
However when I try to reinstall previously bought active content from Amazon, I can't see these contents.
When I change it to default (ie ~ ChangeLocale en-US.utf8 ), I can install this apps again.
Then I think that maybe this could be a way for a nonUS Kindle to install active content specified to US (if it is not possible already) ?
(To buy them from amazon you should change location to US, and access to your account in amazon with a US proxy once at least )