For most practical purposes in photography, a liter and a U.S. quart are close enough to be considered the same. You don't have to follow dilution instructions to the letter. Just be consistent.
Now, people will likely jump in with the numbers to prove how dead wrong I am, and of course, they are right...but keep in mind that I said "most practical purposes in photography". A slightly weaker dilution of all the chemicals I know will not significantly alter their effectiveness.
Even though I am in the U.S., I use liters for all of my measurements. It is so much more easy and sensible.