How do I get translated label for a base field definition?
There are two possible translation methods for a base field, interface translation and configuration translation.

Base fields are defined in code and translated by t(), which gets the translatable string from the core interface translation table.

$translatableMarkup = t($label, [], ["langcode" =&gt; $langcode]);
//optionally, render to string
$translatedLabel = $translatableMarkup-&gt;render();


If a base field override exists in configuration, then it contains a translatable label:

// Override language before loading field configuration.
$language = \Drupal::languageManager()-&gt;getLanguage('fr');
\Drupal::languageManager()-&gt;setConfigOverrideLanguage($langu‌​age);

$field_override = BaseFieldOverride::loadByName('entity_type', 'bundle', 'myField');
if ($field_override) {
  $label = $field_override-&gt;getLabel();
}