I created file with UTF-8 encoded content (using PHP fputcsv).
When I open this file in Notepad++ - characters are wrong (Notepad++ starts with ANSI encoding).
You have to check the lower right corner of the Notepad++ GUI to see the actual enconding that is being used. The problem it's not that Notepad++ specific because guessing the right encoding is a big problem without any real solution so it's better to let the user decide what is the most appropriate encoding in each single case.