default coding systems problem in Windows 10

[Guido Van Hoecke <guivho@gmail.com>]

My emacs running under Windows 10 exhibits a problem with default coding
system. Following text is an example that occurs when starting emacs:

--> These default coding systems were tried to encode text
--> in the buffer ‘ *temp*’:
-->   (iso-latin-1-dos (2145 . 8217) (2169 . 8217) (2185 . 8217) (2209
-->   . 8217) (2226 . 8217) (2250 . 8217))
--> However, each of them encountered characters it couldn’t encode:
-->   iso-latin-1-dos cannot encode these: ’ ’ ’ ’ ’ ’
-->
--> Click on a character (or switch to this window by ‘C-x o’
--> and select the characters by RET) to jump to the place it appears,
--> where ‘C-u C-x =’ will give information about it.
-->
--> Select one of the safe coding systems listed below,
--> or cancel the writing with C-g and edit the buffer
-->    to remove or modify the problematic characters,
--> or specify any other coding system (and risk losing
-->    the problematic characters).

I answer the mini-buffer prompt with 'utf-8' and it proceeds.

I've been googling around, but can't find why, how or where I should
tell it that utf-8 is my default coding system. Never had this problem
with Emacs on OSX nor on various Linux distros. In fact, I'm using the
same .emacs in an LXLE virtualbox (with some conditional path stuff, of
course) and that emacs never complains nor hesitates about coding
systems.

The example above shows that we're even not talking about a physical
file: the problem occurs with a *temp* buffer!

Anny suggestion, any one?

Version: GNU Emacs 25.0.92.1 (x86_64-w64-mingw32) of 2016-03-03
My W10 is an english one, with 'Dutch (Belgium)' for 'date, time and
number formats'


TIA,

Guido