The name of the drowned player is not localized, while the name of the zombie player is displayed directly.
I think it should be "Zombie Name".

The issue with the drowned names appears to only be an issue with the 1.18 version from my testing, and should be fixed as of version 1.18.2-1.1.5e.

The zombie player's name, is working as intended as far as I can see, it should only display the player's name as the nameplate, then the localized name in chat, if it's not working for you feel free to let me know and reopen this issue.