Hello, I made a quick ePub translator script in Python.
It uses Google Translate API (requires credentials in PATH).
Link is here:
https://github.com/Poyeyo/epub-translate
It can translate all text, or it can output both original and translation as parallel texts.
As described in the readme, the resulting file needs to be fixed in Calibre e-book editor or other tool. But the fixes are quick and take almost no time.
Attached is one resulting file with parallel texts.