When going to "Settings-Mail server" and adding all the server details, nothing happens after saving and clicking on "Send test email".

Made a parallel installation of v8.2.1 on the same localhost it works without problems.

ps: Also editing a country ís not working, always get the error "Country name is missing!" although it's set correctly and I wanted just edit the native name.

Thanks for feedback.
Country - it's bug, will be fixed
Mail server - enable error log and check your errors, check also network tab what is response.

Okay, thanks will check and let you know.

With Country same error here but as you mentioned it is a bug....
Mail test works without issues.....

I tested mail server and got error too.
But that error was valid - smtp auth failed, however thrown in ajax response that should be json.

So there will be few updates related to this button and ajax call so error is visible, but will try to implement also some enhancement to mail server so that error can be returned