Sometimes you have to add a new language in Drupal 8/9 programmatically. For example, maybe you need to write an update hook that will add a new language. This is how you can do it:
use Drupal\language\Entity\ConfigurableLanguage; $language = ConfigurableLanguage::createFromLangcode('sr'); $language->save();
If you don't know the langcode, you can find it by inspecting the select box on the /admin/config/regional/language/add page.