Hear me out, he speaks perfect English. He doesn’t speak to the media because the media is just in it for the clicks and he doesn’t care for the spotlight.
Secondly, he keeps this up because he wants his best friend with him there at all times. Maybe it’s a comfort thing, but they have a close bond and if Ohtani was speaking English they would argue there is no need for a translator, thus he losses out on time with his friend!
In Japan English is everywhere and while we aren’t exactly sure exactly where Ohtani grew up it wouldn’t surprise me that he at least knows the basics. My friend from Japan agreed.
Source: trust me bro I’m very wrong