There are scenarios when you work with DVCS (like Mercurial or Git) and CDbMessageSource. To my experience keeping the development database and production database in sync can be very time consuming. Plus, when working in a team, you never know when the database was updated.
In Yii 2.0, the yii widgets that use Twitter Bootstrap CSS & JS directly, are part of the yii2-bootstrap extension, starting with yii/bootstrap namespace. For customizing bootstrap extension specific widget assets, you could configure your own assets (CSS/JS) using the new Yii Asset Manager in your Yii Config file. Something like: