Translation:Two litres of milk are not sufficient.
I will argue that "Two liters of milk is not sufficient" is correct American English (but not British English).
American English typically uses singular verb conjugations for group nouns, and for measured but uncountable mass nouns. So, while "Five oranges is not enough" would not be appropriate, "Five cups of orange juice is not enough" is appropriate American English.
A different example of this in English is referring to an organization or business. American English would say "Duolingo is a company that produces language learning software," while British English would say "Duolingo are...."
Or maybe I'm wrong. :-)