Add multilingual support for site settings

Thanks for the effort you have put into this, this seems like a useful feature to have in place!
I haven't had time yet to test, but just a quick what scanning over the patch:

+++ b/site_settings.module
@@ -8,9 +8,16 @@
+const SITE_SETTINGS_CACHE_CID = 'settings';

I'm nervous that this might be used elsewhere by another module, core etc. It doesn't work to keep it prefixed by the module name?

Ah right I see, that makes sense. I think good to still keep the key (as you have it in your patch) in case we want to eventually use the bin for something else as well.

I've reuploaded this with no changes just to make it apply to the current state of the dev branch. This looks good but needs drush entity-updates in order to work. This therefore needs a hook update so existing installations don't break: https://www.drupal.org/docs/8/api/update-api/updating-entities-and-field...

This set of examples might be helpful
https://www.drupal.org/node/2554097

... and the reupload of the patch

This is unfortunately not something high up on my to do list for now, if someone is willing to contribute a patch to get it there I would be happy to implement, but otherwise I am parking this for now.

Thanks for your work on this - I'll try to take a look sometime in the upcoming week. Will need to get this passing the tests as it needs to have backwards compatibility.

Was just a simple sort order issue in the tests. Will let the test runner run, otherwise this is good to go.

Thanks again for your work on this!

Fixed on dev (was not released).

Can you use a .patch file so it gets unit tested and add interdiffs please next time.
Your patch did not apply and tests didn't run on it.

Hmmm was the other way around for me, was getting fatal errors from the multilingual without multilingual enabled.

I'll take a look in the morning.

Need to keep getting further test coverage in, tried to get a bunch of test coverage in this morning but it wouldn't yet cover repeated saving.

It appears the token had an incorrect type. Your change made it fail coding standards unfortunately as coding standards expects type casting which is why array made it in. I've switched that to string:

 /**
  * Convert the token key into a more readable label.
  *
- * @param array $key
+ * @param string $key
  *   The token key.
  *
  * @return string
  *   A more readable label.
  */
-function _site_settings_token_label(array $key) {
+function _site_settings_token_label($key) {
   $label = str_replace(['--', '-', '_'], ' ', $key);
   $label = rtrim($label);
   $label = ucwords($label);

For the other issue, I can't reproduce it. Have you run 'drush updb'? There was a pending entity update.
As far as I can see from the code, user_id behaves exactly like fieldset - based field save on entity form:

src/Form/SiteSettingEntityForm.php

    // Save the entity.
    $entity = $this->entity;
    $entity->set('fieldset', $values['fieldset']);
    $entity->set('user_id', $values['user_id'][0]['target_id']);
    $entity->save();

and set as a base field in the entity:
src/Entity/SiteSettingEntity.php

    $fields['user_id'] = BaseFieldDefinition::create('entity_reference')
      ->setLabel(t('Authored by'))
      ->setDescription(t('The user ID of author of the Site Setting entity.'))
      ->setRevisionable(TRUE)
      ->setSetting('target_type', 'user')
      ->setTranslatable(TRUE)
      ->setDefaultValue('')
      ->setDisplayOptions('view', [
        'label' => 'hidden',
        'type' => 'author',
        'weight' => 0,
      ])
      ->setDisplayOptions('form', [
        'type' => 'entity_reference_autocomplete',
        'weight' => 5,
        'settings' => [
          'match_operator' => 'CONTAINS',
          'size' => '60',
          'autocomplete_type' => 'tags',
          'placeholder' => '',
        ],
      ])
      ->setDisplayConfigurable('form', TRUE)
      ->setDisplayConfigurable('view', TRUE);

like fieldset

    $fields['fieldset'] = BaseFieldDefinition::create('string')
      ->setLabel(t('Fieldset'))
      ->setDescription(t('The fieldset of the Site Setting entity.'))
      ->setSettings([
        'max_length' => 50,
        'text_processing' => 0,
      ])
      ->setDefaultValue('')
      ->setDisplayOptions('view', [
        'label' => 'above',
        'type' => 'string',
        'weight' => -4,
      ])
      ->setDisplayOptions('form', [
        'type' => 'string_textfield',
        'weight' => -4,
      ])
      ->setDisplayConfigurable('form', TRUE)
      ->setDisplayConfigurable('view', TRUE);

As this issue will automatically close, could please open a new issue if you still encounter the error? Thanks!

I know this is closed, but potential change coming in https://www.drupal.org/project/site_settings/issues/2924674 and want to give others using this on a multilingual site a chance to review. Either way I'll review and try to ensure adequate test coverage.