public function scanParents(string $sourceDir): array
    {
        $locales = $this->scanLocales($sourceDir);
        $fallbacks = [];

        foreach ($locales as $locale) {
            $content = \file_get_contents($sourceDir.'/'.$locale.'.txt');

            // Aliases contain the text "%%PARENT" followed by the aliased locale
            if (\preg_match('/%%Parent{"([^"]+)"}/', $content, $matches)) {
                $fallbacks[$locale] = $matches[1];
            }
        }

        return $fallbacks;
    }