Why is there no translation for the language 'en_US'?

Here is my config.ini

resources.locale.defaul开发者_开发百科t = "en"
resources.translate.adapter = "gettext"
resources.translate.data = APPLICATION_PATH "/../languages/"
resources.translate.option.scan = "directory"
resources.translate.registry_key = "Zend_Translate"
resources.translate.disableNotices = true
resources.translate.default = en

And my languages are structured like in the manual:

application/
languages/
-- en/
---- LC_MESSAGES/
------ default.po
-- se/
---- LC_MESSAGES/
------ default.po

Any ideas ?

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This happens when your translation file for en_US contains only original strings. You need to translate at least one string from original to translated version, compile your *.po to *.mo again, and then it'll start working. If not, rename default.mo to messages.mo, or try even renaming the directory en to en_US.