In fie qa-top-user.php the qa_lang_html('addon/top_user'), is searching for the correct language string.
My solution would be to use the existing misc-language file:
1. In qa-top-user.php change string from: qa_lang_html('addon/top_user'),
to: qa_lang_html('misc/top_user'),
2. open \qa-lang\qa-lang-misc.php and add in the end (within the array):
'top_user' => 'Top Users',
3. save and upload to your server.