Latest snapshot will not show any worlds to load. They do not appear in the available list, nor will typing the world name enable the world to then load. Previous snapshot was fine - so looks like there's something been knocked out.
Comments 3
It being the April fools version that has a different world gen / more dimensions, you should not load common worlds anyway. WAI.
This is intentional. The 20w14infinite worlds use a 'special-level.dat' file whereas 20w13b and below use 'level.dat'