private function fillMissingKeys($fileName, array $foundMissingKeys, $languageKey)
    {
        $missingKeys = [];

        foreach ($foundMissingKeys as $missingKey) {
            $missingKeys[$missingKey] = [$languageKey => ''];

            $this->output->writeln("\"<fg=yellow>{$fileName}.{$missingKey}.{$languageKey}</>\" was added.");
        }

        $this->manager->fillKeys(
            $fileName,
            $missingKeys
        );
    }