Problems when using Vietnamese

[1Dung]

Hi, I just installed manimgl. My first problem is using Vietnamese in TexText class. I don't know how to use Vietnamese, after some self-discovery, I did the following:

1. Add \usepackage[utf8]{vietnam} in line 7 of tex_templates.yml file
2. Edit line 105 in tex_file_writing.py file to tex_path.write_text(full_tex, encoding="utf-8")

After that, I use

t = TexText("Sao thế, vấn đề")
self.add(t)

. But the image shows that characters like "ế", "ề" are not clear. You can see the image I attached. I don't know how to solve it, any help is appreciated. Thanks