Function flattenFiles in making problems

Could you please add verification code to verify if locale code is not yet present in filename??

something like this is working form me:

  public static function flattenFiles($files, $outputPath, $locale, $filesystem, $addLocale = true)
    {
        foreach ($files as $file) {
            $flatName = preg_replace('#[\/\\\]#', '', $file->getRelativePath()).$file->getFilename();

            if ($addLocale) {
                if(!in_array($locale, explode('.', $flatName))){
                    $flatName = preg_replace('#\.xlf#', '.'.$locale.'.xlf', $flatName);
                }
            }

            $filesystem->copy($file->getRealpath(), $outputPath.'/'.$flatName);
        }
        return true;
    }

this is about function in this path: /Translation/Extractor/Util/Flattenizer.php
I hope I'm clear in this explanation if not please let me know.

Open Translation/Extractor/Util/Flattenizer.php and inspect the flattenFiles function, especially how $flatName is built when $addLocale is enabled. Verify the locale check against filenames and confirm that flattening adds the locale only when it is not already present.