index.php

<?php
  
  namespace Test;

  enum Locale: string 
  {
    case en_GB = 'en_GB';
    case de_DE = 'de_DE';
    case fr_CA = 'fr_CA';

    public static function fromLocaleString(string $locale): self
    {
        $parts = \Locale::parseLocale($locale);

        $myOne = $parts['language'] . '_' . strtoupper($parts['region']);

        return self::from($myOne);
    }
  }

  foreach ([
    'de-DE',
    'de-CH',
    'en-US',
    'fr_CA.ISO-8895-1@euro',
    'fr-CA-u-ca-gregorian-nu-arab',

  ] as $localeString) {

try {
  $locale = Locale::fromLocaleString($localeString);

  echo $locale->value . ' selected' . PHP_EOL;
} catch (\Throwable) {
  echo 'Invalid Locale ' . $localeString . PHP_EOL;
}
  }