Gender neutral terms at MWS, also will be translated gender neutral?

In terms of Traditional Chinese, there won’t be an issue on this. In TC it’s called “單身派對／聚會,” which literally means “single’s* party/gathering.” And it has never been a term that has a gender connotation.

*The Chinese language oftentimes operates on an “implied” basis. In this instance, “single’s party” is generally implied as “last night being single.”