Implement hook_entity_create() to setup the default entity language

If the form controllers sets the language to the default language and the language module is not enabled, $entity->language() won't work as the default language cannot be loaded via language_load() then. Everything is fine if the language module is enabled, however we do not want the entity system to depend on that. Right now - in order to work properly - it does. :/

To fix, we need to make sure that $entity->language() is set to a valid value and works. Presuming that language_default() should be valid, I think it should be loadable via language_load() as well then.