Following article will guide you to change database language in MS SQL 2012 server.

1. Login to MS SQL Server 2012 through SQL Management studio with 'sa' user.
   
   
2. Expand the Databases and select the database whom language you want to change.
   
   
3. Right click on the database name, click on Properties.
   
   
   
   
4. Select the Options menu and change the Containment type to Partial from None.
5. Change default Language to your desired language.
   
   
   
   
6. Click on OK button and apply the changes. Restart MS SQL Server through MS SQL Server Configuration Manager.
   
   
7. Again change Containement type to none as described in Step #4.