I had this strange problem that my car was not able to display japanese characters when confronted with them. Oh the marvels of inserting a USB stick into a car from 2009.
Now there’s no real option I know of without risking to brick the car / entertainment system of the car to get it to display the characters right.
Needless so say that my wifes car does the trick easily – of course it’s an asian car!
Anyway. I wrote a command line tool using some awesome pre-made libraries to convert Hiragana-Katakana characters to their romaji counterpart.
You can find it on github: https://github.com/bietiekay/romaji