How can I enforce so Notepad++ uses UTF-8 every time I create a new file?

Go to

Settings -> Preferences -> New Document/ Open Save Directory

and then in

New Document -> Encoding check UTF8 without BOM

You might also want to tick "Apply to opened ANSI files":

screenshot notepad settings


Just bumping once again here at superuser

Step 1: Settings -> Preferences -> New Document ->[Encodng] UTF-8 without BOM (check Apply to opened ANSI files)

but any how it hadn't solved mine , i searched out and found that its a bug!

Notepad++ v6.4.5 bug fixes:

1.Fix a crash issue while there's missing tag in functionList.xml. 

2.Fix UTF-8 (w/o BOM) detection bug.

Step 2: That's all have an update to >= v6.4.5 and follow Step 1