Apparently the story is that the interpreter took Ohtani to a bank and opened an account where all of Ohtani's salary would be deposited. The interpreter then told Ohtani's US based financial advisors that Ohtani denied them access to that account. Ohtani's agent says he asked about the account multiple times but the interpreter always said it was private. This is the apparent explanation as to why no one caught that the interpreter was stealing.
I don't buy it. First, to believe this whole story you have to believe that Ohtani is an absolute idiot. The language barrier can't explain everything away. Who lets their friend convince them to open an account which millions of dollars will be deposited into without their agent or any financial planners involved when you don't understand the language the transaction would be in? I don't believe Ohtani is that gullible. My first reaction in his place would be to have my agent there with me.
Next, I don't buy for a second that the financial advisors and Ohtani's agent would be fine taking the interpreter's word that Ohtani wants his salary deposited into this random account and that they can't see. That structure sets off huge alarm bells for the potential for embezzlement. Ohtani might have trusted the interpreter but there's zero reason why Ohtani's agent or financial people would just trust this guy.
So to buy the story you have to accept that at no point did any of the people around Ohtani try to have a conversation with him about the account his salary was deposited into using a different interpreter. If this was a side account that a relatively small amount of money was going into, that would be one thing. But when his salary is going into this account you don't just take the interpreter's word for it. Getting a Japanese interpreter of your own isn't that expensive.