use Drupal\Core\State\StateInterface;
  /**
  * The state store.
  *
  * @var \Drupal\Core\State\StateInterface
  */
 protected $state;
  /**
  * Drush command constructor.
  *
  * @param \Drupal\Core\State\StateInterface $state
  *   T

Reading State

A single value.

$val = \Drupal::state()->get('key');

Multiple key/value pairs.

$pairs = \Drupal::state()->getMultiple($keys);

Writing State

A single value.

\Drupal::state()->set('key','value');

Multiple values.

Add to file src/Entity/MyEntity.php

/**
* Defines the my entity class.
*
* @ContentEntityType(
...
*   data_table = "my_entity_field_data",
*   translatable = TRUE,
...
*   entity_keys = {
...
*     "langcode" = "langcode"
*   },
...
* )
*/

Add ->setTranslatable(TRUE) to baseFieldDefinitions. For example

Get Language ID

$language = \Drupal::languageManager()->getCurrentLanguage()->getId();

Get Language name

$language = \Drupal::languageManager()->getCurrentLanguage()->getName();

You can remove lock using drush

drush ev "\Drupal::lock()->release('config_importer');"

Use {% trans %} and {% endtrans %}

Use Drupal.t

var optionsList = '<option value="" selected>' + Drupal.t('Navigate...') + '</option>';

/**
* Implements hook_form_FORM_ID_alter().
*/
function mymodule_form_user_register_form_alter(&$form, FormStateInterface $form_state, $form_id) {
 $form['actions']['submit']['#submit'][] = '_mymodule_user_register_form_submit';
}

/**
* Implements hook_preprocess_HOOK().
*/
function EXAMPLE_preprocess_page_title(&$variables) {
 $current_path = \Drupal::service('path.current')->getPath();
 if ($current_path == '/user/login') {
   $variables['title'] = '

/**
* Implements hook_local_tasks_alter().
*/
function EXAMPLE_local_tasks_alter(&$local_tasks) {
  $local_tasks['entity.user.edit_form']['title'] = new TranslatableMarkup('Personal data');
}