The Locale Component

// Get the country names for a locale or get all country codes
$countries = Locale::getDisplayCountries('pl');
$countryCodes = Locale::getCountries();

// Get the language names for a locale or get all language codes
$languages = Locale::getDisplayLanguages('fr');
$languageCodes = Locale::getLanguages();

// Get the locale names for a given code or get all locale codes
$locales = Locale::getDisplayLocales('en');
$localeCodes = Locale::getLocales();

// Get ICU versions
$icuVersion = Locale::getIcuVersion();
$icuDataVersion = Locale::getIcuDataVersion();