Here some simple steps to convert multiple files via Notepad++ without messing up with special characters (for ex. diacritical marks).
Run Notepad++ and then open menu Plugins->Plugin Manager->Show Plugin Manager
Install Python Script. When plugin is installed, restart the application.
Choose menu Plugins->Python Script->New script.
Choose its name, and then past the following code:
convertToUTF8.py
After all, run the script
如果要转化为ANSI 就把插件代码改为下面