iMac voiceover and spoken content unable to switch reading voice based on mouseover

User has impaired vision and is a Windows user.

We switched him to apple iMac because he is comfortable with Siri.

He uses the computer to read his work emails.

While trying to set up voiceover / spoken content, we encountered difficulty getting the iMac to switch between reading voices, e.g. Samantha, Kyoko, when mouseover -ing English and Japanese language in the same email.

Please advise what we did wrong because we remember it worked previously.

Kyoko voice is terrible at reading English words. Samantha ignores japanese characters entirely.

Please help. Thank you.