I was searching for a plugin/gem solution to extend the native rails i18n for storing my translations into my database. Maybe I used the wrong search terms, but all I found
I finally found what I was looking for with the help of Sven Fuchs:
http://github.com/dylanz/i18n_backend_database/tree/master
This quite awesome plugin by Dylan Stamat does exactly what the name indicates and additionally handles the caching!
Sven also mentioned, that the current branch of i18n/active_record provides an ActiveRecord backend as well:
http://github.com/svenfuchs/i18n/blob/active_record/lib/i18n/backend/active_record.rb
Some discussion about this topic is going on in the goolge i18n user group:
http://groups.google.com/group/rails-i18n/browse_thread/thread/6b7ba3c401890a7e
Issue solved, thanks to Mr I18n Sven Fuchs! ;)