src/Resource/LocalizedResource.php
protected function walkFallbackChain(array $valueMap, string $localeCode, Environment $environment)
    {
        $loopCounter = 0;
        while (!isset($valueMap[$localeCode])) {
            $localeCode = $environment->getLocale($localeCode)->getFallbackCode();
            if (null === $localeCode) {
                // We reached the end of the fallback chain and there's no value
                return null;
            }

            ++$loopCounter;
            // The number is arbitrary
            if ($loopCounter > 100) {
                throw new \RuntimeException('Possible endless loop when trying to walk the locale fallback chain.');
            }
        }

        return $localeCode;
    }
protected function walkFallbackChain(array $valueMap, string $localeCode, Environment $environment)
    {
        $loopCounter = 0;
        while (!isset($valueMap[$localeCode])) {
            $localeCode = $environment->getLocale($localeCode)->getFallbackCode();
            if (null === $localeCode) {
                // We reached the end of the fallback chain and there's no value
                return null;
            }

            ++$loopCounter;
            // The number is arbitrary
            if ($loopCounter > 100) {
                throw new \RuntimeException('Possible endless loop when trying to walk the locale fallback chain.');
            }
        }

        return $localeCode;
    }
@param array       $valueMap
@param string      $localeCode
@param Environment $environment

@throws \RuntimeException If we detect an endless loop

@return string|null the locale code for which a value can be found, or null if the end of the chain was reached