Currently, there is a very annoying bug in Rails (at least in 3, dunno about 2) which completely messes up your nice i18n setup in production environments. If you have set cache_classes set to true, all i18n strings in your model classes will fall back to the default locale (EN that is) because the i18n subsystem is not yet initialized when classes are loaded eagerly.
See this bug for reference. Although it is already fixed, it seems like it did not make its way into the recent Rails 3.0.4. release. Luckily, I can present you a workaround here :)
Simply put the following in your application.rb or the respective environment configuration:
# THIS IS A WORKAROUND FOR A I18N BUG IN RAILS!
# Only required when cache_classes is set to true
# See https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/6353
I18n.locale = :de
I18n.load_path += Dir[Rails.root.join('config', 'locales', 'de.yml').to_s]