In system.def at the start of the file you should find something like this:
[Files]
spr = system.sff ;Filename of sprite data
snd = system.snd ;Filename of sound data
logo.storyboard = ;Logo storyboard definition (optional)
intro.storyboard = ;Intro storyboard definition (optional)
select = select.def ;Character and stage selection list
fight = fight.def ;Fight definition filename
font1 = f-4x6.def ;System fonts
font2 = f-6x9.def ;System fonts
font3 = jg.fnt ;System fonts
You should add a line that says (in my case)
font4 = leveis.fnt
(change the numbers accordingly in case you have more than 3 font files)
Then scroll down until you find something like this:
;Stage select
stage.pos = 160,237 ;you have your own, don't care about this.
stage.active.font = 3,0,0
stage.active2.font = 3,2 ;Second font color for blinking
stage.done.font = 3,0
Be sure to write:
stage.active.font = 4,0,0
stage.active2.font = 4,2
stage.done.font = 4,0
in other words you have to change the first number.
Since in my example the font number is 4, I have to change the active font number (for the stages) to 4.