Using language constants in external file

Question

How can I use language constant like JText::_('MY_STRING_FROM_INI_FILE') in external file?

UPD: I include joomla system files

require_once JPATH_BASE . '/includes/defines.php';
require_once JPATH_BASE . '/includes/framework.php';
require_once JPATH_BASE . '/libraries/joomla/factory.php';

$db = JFactory::getDbo();
$app = JFactory::getApplication('site');
$appUser = JFactory::getUser();

but there is effect. Language constants render like MY_STRING_INI, not value of it.

Answer 1

Your language files are not loaded. Load them with Joomla\CMS\Language\Language::load(). This example loads administrator/language/en-GB/en-GB.com_content.ini file:

$app = JFactory::getApplication('site');
$app->initialise();
$app->getLanguage()->load('com_content', JPATH_ADMINISTRATOR);