Konniciwa Junko san, I think it depends purely on the phonetics of the Hindi word. That means, first you have to learn the correct Hindi pronunciation....then, you can spell it out in English (Roman) letters.....trying to make the English word sound as close as possible to the original Hindi pronunciation. Just like I wrote "konnichiwa" at the beginning. I dn't think there's any dictionary for that, because there's no one standard Eng spelling for a Hindi word. It all depends on sound/phonetics. In your expression I think the correct spelling should be .... "Mein accha hoon/hun" Hope it helps. :)

I think Google translator takes a few Hindi words spelled out in English and displays them in the Devnagari script. 'Maan achar hoon' doesn't make sense. I think it should me 'Main accha hoon'. It means 'I am good'.