Hi! Thanks for the reminder. Good news: a font with the correct characters is enough to solve the problem. Perhaps the file also needs to be UTF8. The only time I see squares is when the font does not have the extended characters, or is badly specified and falls back to system font which does not have them.
Here’s a sample text file and a modified font to which I quickly added a few characters.
Sadly I won’t be creating expanded fonts with extended characters, but you can use something like Tophat to easily create a font with your required characters from any TTF and use it to replace one of the bundled Strategies fonts. Have fun!