printf doesn´t seem to use a unicode font.
Because it works, try this:

#include <acknex.h>
#include <default.c>

STRING* str1 = "#8";
STRING* str2 = "#8";

FONT* fontArial = "Arial#20b"; // truetype font, 20 point bold characters

TEXT* txtTest =
{
layer = 999;
string = str1;
flags = SHOW;
font = fontArial;
}


function main()
{
var file;

file = file_open_read("file.txt");

file_str_readtow(file,str1," ",200);
file_str_readtow(file,str2," ",200);

file_close(file);

// printf(_chr(str1));
// printf(_chr(str2));
}

no science involved