al_set_fallback_font - Allegro 5 API

       Sets  a font which is used instead if a character is not present.  Can be chained, but make sure there is
       no loop as that would crash the application!  Pass NULL to remove a fallback font again.

       al_set_fallback_font - Allegro 5 API

al_get_fallback_font(3alleg5), al_draw_glyph(3alleg5), al_draw_text(3alleg5)

Allegro reference manual                                                           al_set_fallback_font(3alleg5)

       5.1.12

              #include <allegro5/allegro_font.h>

              void al_set_fallback_font(ALLEGRO_FONT *font, ALLEGRO_FONT *fallback)