You need to change the language files. Follow the last section on this page for details. Make a file qa-lang/custom/qa-lang-main.php and add
'recent_qs_as_in_x' => 'Best answers in ^',
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.