If you hover your mouse over or click on the sizes the corresponding numeric size will be displayed.
I tried to hover, but all it says on the XS and the L is "XS" and "L".
Ahh, looks like they have it fixed:
Size: XS (M Shoe Size 4-5½, F 5-6½)
Size: L (M Shoe Size 10½-11½, F 12-13½)