Fix missing configuration schema

Here are the messages I get when trying to add the block:

The website encountered an unexpected error. Please try again later.

Drupal\Core\Config\Schema\SchemaIncompleteException: Schema errors for block.block.languagedropdownswitcher with the following errors: block.block.languagedropdownswitcher:settings.showall missing schema, block.block.languagedropdownswitcher:settings.tohome missing schema, block.block.languagedropdownswitcher:settings.width missing schema, block.block.languagedropdownswitcher:settings.display missing schema, block.block.languagedropdownswitcher:settings.widget missing schema, block.block.languagedropdownswitcher:settings.msdropdown missing schema, block.block.languagedropdownswitcher:settings.chosen missing schema, block.block.languagedropdownswitcher:settings.ddslick missing schema, block.block.languagedropdownswitcher:settings.languageicons missing schema, block.block.languagedropdownswitcher:settings.hidden_languages missing schema in Drupal\Core\Config\Development\ConfigSchemaChecker->onConfigSave() (line 94 of core/lib/Drupal/Core/Config/Development/ConfigSchemaChecker.php).

Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('config.save', Object) (Line: 227)
Drupal\Core\Config\Config->save() (Line: 280)
Drupal\Core\Config\Entity\ConfigEntityStorage->doSave('languagedropdownswitcher', Object) (Line: 392)
Drupal\Core\Entity\EntityStorageBase->save(Object) (Line: 259)
Drupal\Core\Config\Entity\ConfigEntityStorage->save(Object) (Line: 364)
Drupal\Core\Entity\Entity->save() (Line: 637)
Drupal\Core\Config\Entity\ConfigEntityBase->save() (Line: 358)
Drupal\block\BlockForm->submitForm(Array, Object)
call_user_func_array(Array, Array) (Line: 111)
Drupal\Core\Form\FormSubmitter->executeSubmitHandlers(Array, Object) (Line: 51)
Drupal\Core\Form\FormSubmitter->doSubmitForm(Array, Object) (Line: 585)
Drupal\Core\Form\FormBuilder->processForm('block_form', Array, Object) (Line: 314)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 48)
Drupal\Core\Entity\EntityFormBuilder->getForm(Object) (Line: 27)
Drupal\block\Controller\BlockAddController->blockAddConfigureForm('language_dropdown_block:language_interface', 'progboot2')
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 574)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
call_user_func_array(Object, Array) (Line: 144)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 64)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 656)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)