For translation of more than a couple sentences on demand, you'd more likely translate the epub before you put it on the device, like with the Calibre plugin https://github.com/bookfere/Ebook-Translator-Calibre-Plugin . There are better solutions that have a dictionary for consistent name translations, too.
According to WMT 2014 benchmarks, GPT 4o and Gemini Flash 1.5 are acceptable. I think Gemini Flash 1.5 8B is the most used right now due to price. In my experience, it is pretty good except in name translation and consistency across text which is why pros use translation dictionaries. It will mostly translate idioms which is nice.