Localization: I want the backend: english and frontend in defined language

Install the plugin WP Native Dashboard. Then you can set one language for the front-end in your wp-config.php and each user can choose another one for the back-end.
See Change language of comments template for details and a screenshot.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)