add vietnamese translation

[sungvadan]

Hello,

This is "Vietnam" language translation.

[llupa]

@sungvadan maybe you checked out before label.remember_me was added. Would you be so kind to add it too?

[sungvadan]

@sungvadan maybe you checked out before label.remember_me was added. Would you be so kind to add it too?

Yes of course, I added this one to my PR

[javiereguiluz]

This is a nice contribution. We love adding new languages to the application. Thanks a lot Van Truong! Cảm ơn bạn rất nhiều!