Symfony itself has an internationalization component, and XML or YAML files are used for this. You can still read the translation of a database. Take a look at their documentation regarding:
http://symfony.com/doc/current/book/translation.html
You can use internationalization in both PHP and template files (using Twig). In the first case, after calling the services container internationalization service, just translate so:
$translator->trans('Hi!');
On Twig, just use the filter trans
:
{{ "Hi!"|trans }}