Question: Unicode characters in GUI on linux

I have a gensym routine (gensym = generate symbol) which appends Chinese characters to some base symbols to create 'new' symbols.  This works well on Windows, Mac and tty maple.  But I get all square boxes in the linux GUI.

I know the fonts exist as, on the same machine, it works in tty.  But I have no idea how to tell the GUI to go and use those fonts.  Nor why it isn't.

Amusingly, if I try to paste something from the GUI as MapleMath here on Primes, in the 'paste' box, it shows just fine, but then it says it is invalid Maple.

For example, from the GUI I see

but the same thing in TTY is

(x三0不 + x三1下)^(-M)

and I just did cut-and-paste of the same thing.  By this I mean that I took that output with boxes above, put it into a terminal window, re-copied that, pasted it in here, and voila!

So clearly the issue is with the GUI, and only on linux (Ubuntu 16.04).