When attempting to display Cyrillic characters (or other national character types), if the characters are displaying as black boxes (rather than as the correct characters), then this could be a result of the chosen font not supporting the character type.

In such cases, you could create and use a font that includes all the characters that you want to draw, and in some cases, this will be the only available solution. Alternatively, setting STD-SMALL-FONT to 1 increases the number of character types that the runtime can display by default: it uses the system DEFAULT-GUI-FONT, which includes many more characters than the default system ANSI-VAR-FONT (which is used when the SMALL and MEDIUM variables are set).
Note: Setting this variable may affect how the runtime sizes controls.