You can change in this file
https://github.com/q2a/question2answer/blob/01f57f19b1ff803c914a06f4e385a7da3ee82b8f/qa-include/lang/qa-lang-users.php
Your Q2A site/qa-include/lang/qa-lang-users.php
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.