At http://www.padrinorb.com/guides/localization, setting up I18n is recommended like this:
I18n.locale = :de
However, in config/boot.rb already is this code:
# ## Configure your I18n
I18n.default_locale = :en
I.e. without the before_load block. Given it works fine without the block, the guide should be corrected.
I reckon it is updated but it hasn't been published yet. See https://github.com/padrino/padrino-docs/blob/master/guides/localization.textile#how-to-localize-your-app