translate

let langCode = drupalSettings.path.currentLanguage;
console.log(langCode);

$language = \Drupal::languageManager()->getCurrentLanguage()->getId();
if ($term->hasTranslation($language)) {
  $term_translated = \Drupal::service('entity.repository')->getTranslationFromContext($term, $language);
  $term_title = $term_translated->getName();
}

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();

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

Use Drupal.t

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

$this->t('April', [], ['context' => 'Long month name']),