How to know if a site is Multilingual programmatically?
Searching I found in drupalcontrib a reference to the language_multilingual() function that show the following code:

function language_multilingual() {
  return Drupal::languageManager()-&gt;isMultilingual();
}


So I used Drupal::languageManager()-&gt;isMultilingual(); and it seems that returns the good value.

I'll do tomorrow a test in a not multilingual site to confirm.