core/Lang.php

Depending on why would you want to use the database on the language file is out of my comprehension but let me give you some ideas.

If you're just pulling info from the file than just call the database from the controller get the info from your database and add it to the $data array to be use in a view.

Now if you're trying to add information to the language file from the database than get the info from the database from your controller and open the language file and add the new data to it and save it this will keep your Language file up to date.

The language file is a simple solution to a simple problem. But depending on what you're trying to do you can just put all your language info into the database and pull it when you want too.

If you really want to use the database on the language file than just connect to it the old fashion way is not that hard.

Or explain a little more on what you're trying to do to see if anyone can come up with a solution.