The circuit lacks mains supply and load, but lets assume that they are in the obvious place.
This is basically the standard DIAC/TRIAC circuit with 2 opto-coupler switched
resistances that can be selected, allowing 4 different speed settings. Seems
Was there a question?
One observation: be safe with mains, make sure the circuitry is double-insulated and
physically cannot be touched when live or testing... Observe good PCB trace clearances
between HV and LV (ie lots of clearance, slots under the optoisolators if poss).