If you want to setup your DotNetNuke web site to be used in singe a non-English language, you might follow this check list:

• Start setting up your portal as usual - either as dedicated DotNetNuke installation or an additional portal in shared installation.
   
• Next, you need to install the proper core language pack and install language packs for all localizable extensions being used, usually all modules and skin objects, as well as authentication and html editor providers.
   
• For Telerik RAD editor, you need to download language resource from Telerik, (F)ckEditor does already include all major language resources.
   
• For custom modules installed you need to create translations yourself using the built in language editor - if ll texts are properly derived from a resource files.
   
• In Admin :: languages, make sure, the new language is enabled and fallback is set to English (US).
   
• Switch portal default language (in Admin :: Site settings, DNN 5.5.0 and above: in Admin :: Languages) to the new language and same for preferred language profile property of all user accounts.
   
• In Admin :: Languages, disable Language "English (United States)" to hide the language selector - but do NOT delete!

Done :)