I've been locked out of my laptop and can't input the password. What can I do?

well how did you change the keyboard? Can you change it back? If not find a lettermap of the vietnameze keyboard to regular, maybe putting it in that way will work.

Have you tried rebooting your PC? Rebooting might clear the Vietnamese setting.

did you reset the P-ram?
sometimes that will clear out keyboard mapping, otherwise you may need to do a hardware reset, just hold the power button down so it dings twice (if memory serves)

@majorrich is on the right track, I think. I’d try the PRAM, too, it will clear to default settings.