If you are using the DatePicker form angular-ui simply add the localized js file in the header of your page. An example would be :
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.0.8/angular.js"></script>
<script src="http://code.angularjs.org/1.0.8/i18n/angular-locale_fr-fr.js"></script>
<script src="http://angular-ui.github.io/bootstrap/ui-bootstrap-tpls-0.6.0.js"></script>
You can see a working plunker here