Drupal 7 - changing overall site language

So, as I am used to read and install everything in english, half of the sites we build are actually only in Dutch. That is, overall site language including the admin interface. I rather like to have the admin interface in english, cause you can more easily google the web on any problems using the english system messages.
So then: All the time I start drushing a site install, enabling my module sets, running some features, focusing on the technical design and the custom functionalities we have to build,  and then suddenly realize that the whole lot has to be in Dutch. Or German. Or Latin, or French or Klingon.

Let's all Klingon

So, how did we change the site language again?

1. Enable the Locale module
2. Download Localization update
3. Enable Localization update
(didn't expect that eh?)
4. Go to Configuration > Languages
(/admin/config/regional/language)
5. Add the language of your choice
(The module will then import the Drupal translation files for the core and all installed modules)
6. Change the default language and Voila, as the French say, your site language has changed.