You can use the Dataface_Application::addJSStrings() method to push translations up to Javascript for their use.
Then use the xataface.lang object.
$app->addJSStrings(array(
'themes.g2.VIEW_SEARCH_RESULTS' => df_translate('themes.g2.VIEW_SEARCH_RESULTS', 'View Search Results'),
'themes.g2.SEARCH_RESULTS' => df_translate('themes.g2.SEARCH_RESULTS', 'Search Results'),
'findwidgets.date.from' => df_translate('findwidgets.date.from', 'From'),
'
findwidgets.date.to' => df_translate('
findwidgets.date.to', 'to')
));