I'm working on a program that is writing a UTF-8 text file. This process works fine. What doesn't work fine is that TextEdit.app (and others) does not recognise it automatically as a UTF-8 text file, ...

ANSI and UTF-8 are two types of text encoding. The former is the default encoding that is used when you save text files created in Notepad, the text editor included in the Windows operating system.