As you can see in the screenshot below, there is an empty space inbetween the alerts.
This alerts is supposed to read:
Multilingual Sample Data has been installed!
Apparently you did not install Multilingual sample data but the testing sample data and although there is obviously a bug with empty space, the last message correctly display "Testing Sample Data has been installed".
The white space has the message "Multilingual Sample Data has been installed!" hence the comment.
However this can be closed as a duplicate of #25777
Apparently you did not install Multilingual sample data but the testing sample data and although there is obviously a bug with empty space, the last message correctly display "Testing Sample Data has been installed".