I think the library doesn’t include the Asian fonts so this issue happen.
I found a reference only for the UDK, do anybody have ideas for doing the same things in UE4? http://udn.epicgames.com/Three/ImportingFonts.html
Its later reply, but it might be useful for someone having this issue.
You need to import custom font that supports Chinese characters. In font details you should add in Unicode Range range of unicode block of these characters you need.
I am not familiar with Chinese language, so I can’t tell you what block exactly you should put, but you should be able to figure it out from here: ✔️ ❤️ ★ Unicode Character Table