https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21StringTranslation%21TranslationManager.php/function/TranslationManager%3A%3AsetDefaultLangcode/11.x
function TranslationManager::setDefaultLangcode | Drupal API
functiondrupalapi
https://api.drupal.org/api/drupal/core%21modules%21language%21src%21Entity%21ContentLanguageSettings.php/function/ContentLanguageSettings%3A%3AsetDefaultLangcode/9
function ContentLanguageSettings::setDefaultLangcode | Drupal API
functiondrupalapi