Some document have non-standard locale code

src/PhpWord/Style/Language.php

@@ -228,6 +228,8 @@ final class Language extends AbstractStyle
      */
     private function validateLocale($locale)
     {
+        $locale = str_replace('_', '-', $locale);
+
         if (strlen($locale) === 2) {
             return strtolower($locale) . '-' . strtoupper($locale);
         }