Is there any plugin which allows only to create new tags if user has 50+ reputation?
Yes. Tagging tools plugin here: https://github.com/svivian/q2a-tagging-tools
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.