Don't worry, there are lots of English speaking passengers on a cruise out of Singapore. Probably more than Mandarin as English is the administrative language.
In terms of demographic, you shouldn't see that many mainland Chinese parties or guests, because they're still opening up. But expect more Indians, Singaporeans, Malaysians and Expats from Singapore as well as further out international passengers and you're good to go!
Try and practice ya mandarin and have a go with the crew onboard, i'm sure they'll be more than willing to entertain it! Enjoy your cruise 🙂