How to install Drupal 7 in a language other than English

If you want to install Drupal in a language other than the default English, you have to do some fiddling on the command line to make your favorite language available to the installer. First, you have to decide which installation profile you are going to use. In the default download, there are the two profiles minimal and standard. Chances are you will want to go for the standard one as this has a number of useful modules installed and activated.
In the profile's directory profiles/standard, create a new directory translations. To this new directory, you have to copy your language file downloaded from ftp.drupal.org . You have to make sure that you download the file that matches your language and core version. For the German language file and the latest alpha version of Drupal 7, this is the file drupal-7.0-alpha6.de.po. Download the file and place it into profiles/standard/translations. You have to rename the file to just the ISO code for your language, in case of German the file path will become profile/standard/translations/de.po .
Once you have this file in place and invoce the Drupal installer, it will offer you your language in addition to the standard English as a choice after the profile selection.