eli5 how do people with names that use non-english characters decide the spelling of their romanized name?

Question

for example if someone with a Japanese name needs to write it using the English alphabet (perhaps for a legal document?) do they get to decide what letters will work best or maybe is there a general system they’ll use to translate it over? this is not limited to my example, I am curious about other languages that use characters as well!

In: 12

Answer 1

[removed]