I have a font with europeean characters in the range 0x80 to 0xff (ANSI, Windows-1252-encoding). The editor/compiler however, always encode C-strings in UTF-8 so the europeean characters diplays as garbage on the display. How can I tell the compiler to stick to ANSI (Windows-1252) as plain Visual Studio does? The file is saved as ANSI, no UTF-encoding.
Also, if I build the code in Visual Studio Code it works as it should and displays all characters correctly.

Thanks for the reply but saving the file as UTF-8 is already tried.
It can never work as the font file is in Windows-1252-encoding with one byte per character.
The compiler encodes the string "åäö" as:
0xEF 0xBF 0xBD 0xEF 0xBF 0xBD 0xEF 0xBF 0xBD 
which is UTF-8 for "replacement character". This seems to point out that Arduino/Visual Micro cannot handle characters above 0x7f which suggests that you have to use UTF-8 (which breaks the code in another way). Strange, as VS Code & PlatformIO performs ok with those characters.
I use Visual Studio with Visual Micro using Arduino IDE 2 or Visual Micro (no IDE).
I'm using a 1.8 TFT display with 
#include <Adafruit_GFX.h>
#include <Adafruit_ST7735.h>
which works ok with VS Code & PlatformIO with the .ino file saved with Windows-1252-encoding.

Edit:
I also tried with Arduino IDE stand-alone. It works as well. It is only Visual Micro which refuses to understand character codes above 0x7f if not encoded as UTF-8 (which then will not work with the display).

Can you install the latest release from the top of the below board:
https://www.visualmicro.com/forums/YaBB.pl?board=VS_ARDUINO_EXT_RELEASES

Then if you add a local board.txt to your project (vMicro > Add Code > Add Local Board.txt) and paste in the below entry:
vm.compiler.use_file_own_encoding=true

Also ensure the INO file (and any others affected) are saved with the correct ANSI encoding as desired (using File > Save As > Save with Encoding).

Then if you restart Visual Studio and rebuild your project, the encoding should persist through the compilation process.

The setting will most likely become default after we have tested with different IO boards. Windows/linux programs and an embedded program have different constraints to be careful of.