Enable translation for theme settings

Question

Theme settings are not translatable in core. Is there a way to make them translatable? I have some additional theme settings which needs to have different values per language.

I'm trying to achieve something like this - How do I translate theme settings?

What I have so far -

mytheme/config/schema/mytheme.schema.yml

mytheme.settings:
  type: theme_settings
  label: 'My theme settings'
  mapping:
    custom_textarea:
      type: text_format
      label: 'Additional settings'

mytheme/config/install/mytheme.settings.yml

custom_textarea:
  value: "<p><sup>*</sup>this is an additional settings.</p>\r\n"
  format: full_html
langcode: en

mytheme/mytheme.config_translation.yml

mytheme.settings:
  title: 'my theme settings'
  base_route_name: system.theme_settings
  names:
    - mytheme.settings

theme-settings.php

/**
 * Implements hook_form_system_theme_settings_alter().
 *
 * Form override for theme settings.
 */
function mytheme_form_system_theme_settings_alter(array &$form, FormStateInterface $form_state) {


  $custom_textarea = theme_get_setting('custom_textarea');
  $form['custom_textarea'] = [
    '#type'          => 'text_format',
    '#title'         => t('custom textarea'),
    '#format'        => 'full_html',
    '#default_value' => $custom_textarea['value'],
  ];


}

When I navigate to admin/config/regional/config-translation it shows the 'my theme settings' but when I click on Translate it navigates to admin/appearance/settings/translate and returns Access Denied.

I also tried updating the base_route_name in mytheme.config_translation.yml to system.theme_settings_theme but when I navigage to admin/appearance/settings/mytheme/translate it throws a fatal error.

Looking forward for any suggestions.

Answer 1

in schema change field type to text and add translatable: true

mytheme.settings:
  type: theme_settings
  label: 'My theme settings'
  mapping:
    custom_textarea:
      type: text
      label: 'Additional settings'
      translatable: true

You may also face this problem later https://www.drupal.org/project/drupal/issues/2719553 (my reply there is the last from current date)