Add Vietnamese lang please

[dieucq]

Please add Vietnamese lang into your code,I input the Vietnamese (ngày mai em đi,...) but output is error as shown in picture.
Thank you.

[lyqht]

hi, by error, do you mean that the text you got from scanning the qr is different from your input?

if you know how to fix it, feel free to open a PR!

[dieucq]

I think this error is caused by unicode font at server side, don't know if i can fix it or not, just open issue and hope you can help with that.
Thank you.