Hi, thanks for pointing out this error.
I'm not able to test the Linux build myself, but from what I can tell you might be able to fix this by setting the launch options with the following command:
mkdir fonts; echo '<fontconfig><dir>/usr/share/fonts</dir><cachedir>fonts</cachedir></fontconfig>' >fonts/fonts.conf; FONTCONFIG_PATH=fonts ./nw # %command%
Still doesn't work. This time it looks like a crucial file is missing in a "img" directory. I think the issue is that there are crucial files missing from the Linux build of the game, though I wouldn't know since I have very little game dev experience and also haven't worked with RPG Maker before. But at the very least, the game's window shows up now, which is progress!