A cubic unit represents a volume taken up by one unit of length, width and height. A liter is a three-dimensional unit of volume, not length; therefore, the term "cubic liter" does not make sense.
One can convert between liters and cubic units where the units are measurements of length. For example, 1 milliliter, or 1/1,000 of a liter, is equivalent to 1 cubic centimeter; therefore, 1 liter is equal to 1,000 cubic centimeters. One liter is also equivalent to 1 cubic decimeter. One cubic meter is equal to 1 kiloliter, or 1,000 liters; similarly, 1 liter is equivalent to 1/1,000 of a cubic meter.