Error while running rails 2.0.0. "de" is not a valid locale (I18n::InvalidLocale)

Ho together,

I had some problems with utf8 and ascii, in case of this I tried to update from ruby 1.9.3 to ruby 2.0.0

that worked but now when I want to start my app I got this error:

/home/felix/.rvm/gems/ruby-2.0.0-p643/gems/i18n-0.7.0/lib/i18n.rb:284:in `enforce_available_locales!': :"de-DE" is not a valid locale (I18n::InvalidLocale)
    from /home/felix/.rvm/gems/ruby-2.0.0-p643/gems/i18n-0.7.0/lib/i18n/config.rb:34:in `default_locale='
    from /home/felix/.rvm/gems/ruby-2.0.0-p643/gems/i18n-0.7.0/lib/i18n.rb:35:in `default_locale='
    from /var/www/xyz/xyz/config/application.rb:79:in `<top (required)>'
    from /home/felix/.rvm/gems/ruby-2.0.0-p643/gems/railties-3.2.12/lib/rails/commands.rb:53:in `require'
    from /home/felix/.rvm/gems/ruby-2.0.0-p643/gems/railties-3.2.12/lib/rails/commands.rb:53:in `block in <top (required)>'
    from /home/felix/.rvm/gems/ruby-2.0.0-p643/gems/railties-3.2.12/lib/rails/commands.rb:50:in `tap'
    from /home/felix/.rvm/gems/ruby-2.0.0-p643/gems/railties-3.2.12/lib/rails/commands.rb:50:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

I've set the

default_locale: de 

in the settings.yml

Whats going wrong? and how can I fix it? I'm running under debian 7 and rails 3.2.12