Failed to start the User Profile Synchronization service

The User Profile service application stores information about users in a central location. Social computing features use this information to facilitate productive interactions which enable users to collaborate efficiently. In order to provision My Sites, enable social computing features such as social tagging and newsfeeds, and create and distribute profiles across multiple sites and farms, you must enable the User Profile service application.

In the 'Central Administration--Services on the Server page, the User Profile Synchronization Service is in 'Stopped' state. 

Also when you check the ULS log after the entry ILM configuration: Configuring Registry keys, you can see several entries similar to the next:  

"Unable to load Assembly for LCID"

In the Synchronization DB on the SQL server, the User account assigned to the "User Profile Synchronization Service" was not mapped to the login account as 'dbo' in the 'User' and 'Default schema' columns.

Resolution:

1.   Open the Microsoft SQL Server Management Studio from Start - All Programs menu

2.   Under Security, expand logins and select the user account assigned to the user profile synchronization service.

3.   Right click Properties > User mapping > on the right panel, scroll down until you find the User Profile Service Application synchronization DB.

4.   Make sure that it is checked and change the value for the 'User' and 'Default schema' columns to 'dbo.

If you get an error while performing the previous operations, then you should make the changes in the Synchronization DB. Expand the Synchronization DB node > Security > Roles > Database roles and select the 'FIM_SynchronizationService', 'persistencesUsers' and 'state_persistence_users' values.

Delete the FIM certificates and restart the user profile synchronization Service.

Please let me know in case of any further queries/questions. I would be more than happy to help you as well as resolves your issues, Thank you.