Use lv_font_conv to convert Chinese display garbled code

[flashsim]

I use LVGL 9.1.1 version. After using the official online and offline font conversion tools to convert a Chinese character, the demo example shows garbled characters on the LCD. I don't know where the error is. Can you give me some suggestions? thinks

The command to use the offline conversion tool is:
lv_font_conv --no-compress --format bin --font QingNiaoHuaGuangJianMeiHei-2.ttf -o my_font-guo.bin --bpp 4 --size 30 --symbols "国"

I used the online method to save the bin file and compared it with the bin file generated above. The generated bin files are the same.
the test code is:
void lvgl_font_test(void)
{
lv_font_t * font_18 = lv_binfont_create("0:my_font.bin");
if (font_18 == NULL)
{
printf("font load failed \r\n");
return;
}

lv_obj_t *label_name = lv_label_create(lv_screen_active());
lv_label_set_text(label_name, "国");
lv_obj_set_style_text_color(label_name, lv_color_hex(0x003a57), LV_PART_MAIN);
lv_obj_set_style_text_font(label_name, font_18, LV_PART_MAIN);
lv_obj_align(label_name, LV_ALIGN_CENTER, 0, 0);

lv_binfont_destroy(font_18);

}

[Christer-Ekholm]

My first try debugging test would be

lv_font_conv --no-compress --format bin --font QingNiaoHuaGuangJianMeiHei-2.ttf -o my_font-guo.bin --bpp 4 --size 30 --r 0x56FD

lv_label_set_text(label_name, u8"\u56FD");

I am not sure if those UTF codes are correct because I have worked so little with those.
I am newer trusting encodings of editors and consoles so I would try numerical values first.