I would like to understand the footprint codes used for capacitors in diptrace, especially for the radial components.

for example, what footprint will fit this capacitor: Cap Radial, D-10mm, L-25mm, Pitch-5mm - HORIZONTAL

thanks

It should be CAPPR-5/10h25 but it is for vertical mounted capacitor. Horizontal position has not foreseen but you can give it new name as you want.