There's a simple workaround for this.

Somebody must send you a Red Packet. It can be for RMB1. If you PM me your WeChat ID then I can send you one.

Then, magically, the Wallet function will appear in your Me menu and you can add your Union Pay card and you're good to go.

This trick was told to me when I moved to China six months ago with the "international" (ie English) version of WeChat that didn't apparently have the Wallet function. It worked. I've since done it for others.

Just watch out entering your Union Pay card details. The application is very particular about the name you enter matching the name on the account to the exact upper and lower case letter and spaces between names etc. People have tried and failed because their helpful Chinese bank has entered invisible spaces in the account name between names and after the name. If it fails for you then it's almost-certainly because your account name is not exactly what you think it is.