Although we will talk some more about the multilingual features of Drupal 8, let's briefly note the possibility of the language overrides.
If we enable configuration translation and add some more languages to our site, we can translate configuration items that are translatable (as described by their schema). In doing so, we are overriding the default configuration for a particular language, an override that gets stored in the configuration storage and can be exported to YAML files. So this is an exportable type of override.
We can make use of this override programmatically, even if we are not in a specific language context. This is what the code would look like, assuming we have an override in French for our maintenance mode message and we want to use that:
$language_manager = \Drupal::service('language_manager');
$language = $language_manager->getLanguage('fr');
$original_language = $language_manager->getConfigOverrideLanguage();
$language_manager->setConfigOverrideLanguage($language);
$config = \Drupal::config('system.maintenance');
$message = $config->get('message');
$language_manager->setConfigOverrideLanguage($original_language);
This looks a bit complicated, but it's not really. First, we load the language manager service and get the Language object for our language (the one we want to get the overridden value for). Then, we keep track of the original configuration override language (which is essentially the current language) but also set the French language as the one to be used going forward. Finally, we load the system.maintenance configuration object and read its message in French before restoring the original language on the language manager. This is a quick way to illustrate an approach by which we can temporarily switch language contexts for configuration overrides. And this will be the way to load configuration entities in a different language to the current one.