Hi,

Can one EPUB file support various languages?
Example, an English EPUB file can also be quickly converted to Japanese?

Thank you!

If you use Google translate it can be converted quick. Not readable, but quick.
You cannot create a version that supports multiple language. You can add more versions in the book in different languages, but it would be easier to create multiple books.

You can find here an attempt to create a multilingual ePub. It's much work, and I'm not sure how practical the result is, but there it is.