If your source files are in UTF-8, and the characters you are trying to display are present in the font, you'll get characters displayed correctly. The catch is that only a limited range of characters is supported right now. Support for other character sets (mainly ones that don't require layout support) and built-in translation is planned, but these aren't being developed right now.

The game uses a custom bitmap font, which includes most Latin and derivative writing systems, but it doesn't include many other important Unicode blocks, such as most CJK characters, although it does include the Hangul Syllables block and just enough other syllables to allow for Korean text to be displayed properly (but Korean text input is still rather broken and built-in translation is not a feature yet at all, so this fact gets very little recognition).

For Chinese and Japanese, I've considered bundling zpix, but a fundamental problem that this doesn't address too well is that Chinese and Japanese speakers may expect different characters to be displayed using the same Unicode code points.

There's no good documentation on the custom bitmap font's format, you'll have to read the code and figure out how it works if you want to programmatically add characters to it. And you definitely want to add characters programmatically if you're planning to add CJK characters; I don't suppose you'd want to draw them by hand.

zpix is distributed in the BDF format, and we have a python script that can merge BDF fonts into the codebase. In zpix's case, you can do this by running:

./fonttool.py addbdf 0 1114111 ~/Downloads/zpix.bdf 0 -2

which will give you something like this (text taken from the zpix demo):



Be sure to ask zpix's owner before you publish anything with the font built in, though.

You can't change the size easily (which is to say, it's possible but TPT has no support for it). That's a trait of bitmap fonts: https://en.wikipedia.org/wiki/Computer_font#Bitmap_fonts