The program does not crash for me. Instead I see this:
The solution is to specify a wide string in the string declaration:
auto label2 = CreateLabel(L"Тест", 20, 50, 120, 30, ui->root, LABEL_BORDER | LABEL_CENTER | LABEL_MIDDLE);
Then it looks like this:
(Non-latin characters are currently not supported in a 3D GUI because I have to change the way characters are rasterized from the font. This is on my to-do list.)