Where to put Commerce Kickstart translation po file? After installing a blank Commerce Kickstart site, I'd like install another language as default for the site.

I can see the language .po file to download -> here 

Where should I put the .po files and how can I enable the new language as default?
The internationalization process is not unique to Commerce Kickstart; it is the same for all Drupal sites and handled by the Locale module.  The Drupal.org documentation can be found here.  (Start with Install a language.)